Impact of water status, biochemical and mechanical ...

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We thank the Hans-Böckler-Foundation for the scholarship to Wolfgang Graf and ... Graf, W., O. Schmid, H. Grüneberg, L. Hendriks and S. Huyskens-Keil (2006): ...
5th Plant Biomechanics Conference – Stockholm, August 28 – September 1 2006

Impact of water status, biochemical and mechanical product properties on bent neck occurrence in cut roses Wolfgang Graf1, Susanne Huyskens-Keil2, Werner B. Herppich3 and Heiner Grüneberg1 1Humboldt University Berlin, Institute of Horticultural Sciences, Germany, Section of Floriculture; 2Section of Quality Dynamics/Postharvest Physiology 3Leibniz-Institute of Agricultural Engineering Potsdam-Bornim, Germany, Department of Horticultural Engineering

Abstract Bending of the flower buds (bent neck) is a widespread problem damaging millions of cut roses well before they achieve their genetically fixed vase-life. Structural weakness, reduced cell wall strength or disturbed stem water status are assumed to cause the bent neck phenomenon. However, the exact reasons for this disorder are still unknown. The aim of this investigation was to find parameters during the production period to determine postharvest life. The development of the vascular bundles affects the mechanical bending resistance. This was ascertained for the cultivars ‘Red Giant’ (long vase-life and high bent neck resistance) and ‘Aloha’ (short vase-life and low bent neck resistance) but not for the cultivars ‘Akito’ (short vase-life and low bent neck resistance) and ‘Milva’ (long vase-life and high bent neck resistance). Furthermore, there was a close correlation between the tissue water potential of the upper third of the peduncle and the shelf live of the cultivars ‘Akito’ and ‘Red Giant’ but not found for ‘Milva’. More investigations have to be conducted to explain these different reactions of the cultivars.

Introduction The vase-life of cut roses is largely determined by the postharvest water regime. Particularly, the inhibition of a continuous water supply in the peduncle leads to bending of the flower (bent neck), as described by Burdett [1]. The cultivars ‘Akito’ and ‘Milva’ differ greatly in their resistance to postharvest drought stress [2]. From unpublished investigations by the authors the cultivars ‘Akito’ and ‘Aloha’ have a short vase-life and low bent neck resistance whereas ‘Milva’ and ‘Red Giant’ have a long vase-life and good bent neck resistance. After turgor loss, bending resistance is entirely determined by the mechanical strength of the stalk tissue at the stem section where the neck normally bends. This section is the upper third of the peduncle mainly consisting of young differentiating tissue [3, 4]. Therefore, the mechanical properties of the tissue will be studied in more detail. Cell wall structure and composition are important determinants of strength [3, 5, 6]. Changes in content, biochemical composition and distribution of the different groups of structural carbohydrates have already been studied in detail during flower development of roses [3, 4, 5, 6, 7]. Zamski et al. [6] found that cultivars with strong peduncles showed an extended vase-life, and low bent neck susceptibility. In contrast, weak peduncles may result in a short vase life due to a high probability of bent neck occurrence. Furthermore, vascular bundles arranged in closed rings provide a higher resistance to bending then solitary ones.

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5th Plant Biomechanics Conference – Stockholm, August 28 – September 1 2006 A documentation of the arrangement of vascular bundles at the place of bent neck is missing for new important rose cultivars. In the whole project the arrangement of the structural carbohydrates will be visualized by fluorescence microscopy studies.

Material and methods Plants of the varieties 'Akito' and 'Aloha' (both with a short vase life), and 'Milva' and 'Red Giant' (both with a long vase life) were grown under greenhouse conditions at the Institute of Horticultural Sciences (Humboldt University Berlin, Berlin, Germany). Mean climate conditions were: 20° C air temperature, 23°C aeration temperature, 60% to 80% relative air humidity. Natural light was supplemented with sodium high pressure lamps to yield a minimum light intensity of 10 klx (approximately 140 µmol m-2 s-1) for 18 h. Plants were automatically trickle irrigated with nutrient solution to keep substrate water potential above –70 hPa. With the “Japanese system” (bending down the blind or redundant stalks to get more leaf area for photosynthesis), 8.6 plants per m2 were cultivated in double rows in 7l pots on tables. Roses were harvested at the flower development stage 2, modified from Grszynska et al. [11]. On unstained freshly hand-cut sections from the bent neck susceptible upper third peduncle part arrangement, structure and dimensions of the vascular bundles were examined with a light microscope (magnification 40x, Eduval 30, China). The apparent quasi-static modulus of elasticity [12] was determined by compression tests (v = 100 mm min-1, spherical steel body, diameter = 6.35 mm) at the middle of the upper third of the peduncle part with a material testing machine (Zwicki 1120, Zwick, Ulm, Germany). Finally, mean cutting force over the entire spear diameter (Fcut) was obtained by slicing (crosshead speed 600 mm min-1) the peduncles at the same position as the force deformation measurements with a stainless steel microtome blade (Feather S35, 0.26 mm total thickness) adapted to the material testing machine. Mean cutting force and the true cutting length (Lcut) was used to calculate the total cutting energy (Ecut = Fcut / (Lcut * p/4) which closely indicates tissue strength. The water potential of cross-sections (2 mm thick and 4-8 mm diameter) of this stem part was measured psychrometrically [13] with Wescor C-52 dew point hygrometers connected to a Wescor HR-33T micro voltmeter (Wescor Inc., Logan, USA).

Results and discussion The anatomical examination of the peduncle tissue revealed important cultivar-specific differences in the structure and the arrangement of the vascular bundles (Table 1 and 2). The cultivar ‘Milva’ was characterized by an extremely loose arrangement of the bundles, lacking a true ring structure. Most of the vascular bundles were assorted disjunctively, clearly separated from each other. Only in some rare cases the configuration had a loose wavy structure. Zamski et al. [6] reported a high correlation between the arrangement of the vascular bundles, the occurrence of bent neck and the vase life. According to these authors this should reflect the bundle structure of varieties with a short vase life and high susceptibility to bent neck. In contrast, ‘Milva’ has a very long vase life. On the other hand, the vascular bundle structure of the peduncle of ‘Red Giant’ is very compact. The bundles form an almost closed ring with few openings and with a strongly wavy form like a corrugated iron sheet. This variety shows the most advanced differentiation of the vascular ring in the peduncle. ‘Akito’ has only slightly waved rings with many openings in it. Compared to ‘Akito’ the bundle structure of ‘Aloha’ is much more compact but clearly less than that of ‘Red Giant’. A significant difference in the vascular bundle structure was found only between the cultivar ´Red Giant` and the three other cultivars. The most important result is that ´Milva` (long vase life and high bent neck resistance) has a looser structure than the short vase-life cultivars ‘Akito’ and ‘Aloha’. This is contrary to the results of Zamski et al. [6], who reported a strong correlation of a loose structure and a short vase life.

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5th Plant Biomechanics Conference – Stockholm, August 28 – September 1 2006 Table 1: Rating of the structural arrangement of vascular bundles in stems of the four cultivars (n=20).

Cultivars loosely ring

‘Akito’ ‘Aloha’ ‘Milva’ ‘Red Giant’

Numbers of stems with…. closed closed ring closed lowly wavy strongly ring with many ring with ring wavy without openings few ring openings openings

0 0 11 0

0 0 0 0

17 12 12 2

3 9 0 19

20 12 14 0

0 8 0 20

some solitaire bundles outside the ring 4 19 15 11

Table 2: Rating of the structural arrangement of vascular bundles in stems of the four cultivars (n=20).

Cultivars

‘Akito’ ‘Aloha’ ‘Milva’ ‘Red Giant’

Numbers of stems with vascular bundles being arranged as….

solitaire

in a loose bound

bonded

13 1 19 0

17 20 3 20

0 7 0 13

The water potential of the upper third peduncle is shown in Fig 1. The results from ‘Red Giant’ and ‘Akito’ corresponded well with the vase life and the susceptibility to bent neck. On the other hand, the results from ‘Milva’ were not consistent with their postharvest reaction. According to Graf et al. [2] ‘Milva’ had always a higher flower water potential than the other varieties, which contradicts these data, too. One probable explanation is that the tissue water potential of the peduncles differed from the flower water potential. There is no information published in the literature about the water potential in this part of the rose stem. Furthermore, large differences occurred between the results obtained on the two days. Further investigations are needed.

28.03 Akito

6.04

Aloha

mean value Milva

0.00 Psit [MPa] 20°C

-0.25

Red' 'Giant

Fig. 1 The psychometric water potential in the tissue from the upper third peduncle part (n=5). Measured at two days.

-0.50 -0.75 -1.00 -1.25 -1.50 cultivar

The apparent quasi-static elastic modules of the peduncles were not significant different between the varieties studied (data not shown). The correlation between tissue stiffness and water potential reported for white asparagus [11, 12], and for radish and carrots [10] under different postharvest conditions, could not be verified with cut roses in these initial experiments.

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5th Plant Biomechanics Conference – Stockholm, August 28 – September 1 2006

The mean cutting energy of the upper third peduncle (Fig. 2), which closely reflected the integrated tissue strength of this stem part, was highly and significantly different between ‘Red Giant’ and the three other cultivars. In ‘Red Giant’ these results corresponded well with the structure of the vascular bundle rings. Nevertheless, the assumption that a structure with closed rings and only a few openings, and almost a strongly wavy form provided a higher mechanical strength than a loosely structure is only partially affirmed in this investigation. In this first test, roses of ‘Milva’, which have a low bent neck susceptibility and a loose configuration of vascular bundles, showed the same low strength as ‘Aloha’ and ‘Akito` with their much closer ring structure.

2500

Fig. 2 The mean cutting force resistance of the upper third peduncle part (n=5). Measured at two dates.

Cutting energy (J m

-2

)

means ± standard deviation

2000

1500

1000

500

'M ilv a' 'R 28 ed G ig an t' 'R 06 ed G ig an t' 28

28 'A lo ha '0 6 'A lo ha '2 8 'M ilv a' 06

A ki to '

'A ki to '

06

0

cultivar/date

Conclusion Bent neck is a multifactorial phenomenon, which need to be studied under various aspects. This phenomenon cannot be explained with two cultivars as reported by Zamski et al. [6] for studying the effects of the mechanical strength. The bent neck can be indicated by different factors in the different cultivars. One factor is the mechanical strength investigated here. A second factor is the stomata control in postharvest. Additionally, unpublished investigations indicated that flower stems of ‘Akito’ and ‘Aloha’ showed faster mass losses, i.e. higher transpiration rates under drought stress than ‘Milva’. Accordingly, Schmid et al. [14] reported a less effective stomatal control under drought stress in ‘Akito’ in comparison to ‘Milva’. The four investigated cultivars might be a good basis to approach different factors determining the bent neck susceptibility as they reveal different physiological reactions in postharvest. In further experiments physiological parameters (stem and flower bud water relations, hydraulic conductance, leaf and flower gas exchange concomitant with vase life) will be studied. Furthermore, a more specific look of the anatomical properties in the cross-section of the upper third peduncle part will be

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5th Plant Biomechanics Conference – Stockholm, August 28 – September 1 2006 conducted. Hence, vessel diameter, cell wall thickness, structure and carbohydrate of the peduncle tissue will be investigated in detail.

Acknowledgements We thank the Hans-Böckler-Foundation for the scholarship to Wolfgang Graf and many companies for material sponsoring: The rose nursery W. Kordes, Söhne Klein Offenseth- Sparrieshoop, Germany and Rosen Tantau, Uetersen, Germany for the rose plants and licences, the rootstock nursery Lodder, Dülmen, Germany for the rootstocks, Hermann Meyer, Rellingen, Germany for the pots, Stender AG, Luckau, Germany for the substrate and Braun GmbH, Lemgo, Germany for the Chrysal fresh flower food.

References 1. Burdett, A.N. (1970): The Cause of Bent Neck in Cut Roses. Journal of the American Society of Horticultural Sciences. 95 (4): 427-431. 2. Graf, W., O. Schmid, H. Grüneberg, L. Hendriks and S. Huyskens-Keil (2006): Hydraulische Leitfähigkeit und Wasserpotenzial von Schnittrosensorten. Proceedings of the 43. Annual Meeting of the German Society of Horticultural Science: Potsdam, 22-25 February: 233. 3. Zieslin, N., H.C. Kohl, A.M. Kofranek and A.H. Halevy 1978: Changes in the Water Status of Cut Roses and its Relationship to Bent neck Pheonomenon. Journal of the American Society of Horticultural Sciences.. 103 (2):176-179. 4. Zieslin, N., F. Starkmann and E. Zamski 1989: Bending of rose peduncles and the activity of pheylalanine ammonia lyase in the peduncle tissue. Plant Physiology and Biochemistry. 27 (3): 431-436. 5. Chabbert, B., B. Monties, N. Zieslin and R. Ben-Zacken (1992): Lignin content and composition of rose flower peduncles differing by their resistance to bending. Plant Physiology and Biochemistry. 31 (2): 241-247. 6. Zamski, E., F. Starkmann and N. Zieslin 1991: Mechanical Strength and anatomical structure of the peduncles of rose (Rosa x Hybrida) Flowers. Israel Journal of Botany. 40: 1-6. 7. Parups, E.V. and P.W. Voisey (1976): Lignin content and resistance to bending of the pedicel in greenhousegrown roses. Journal of Horticultural Science. 51: 253-259. 8. Herppich, W.B., B. Herold, S. Landahl, F. Gomez Galindo and M. Geyer (2004): Effects of temperature on produce texture and water status. A model study on radish and carrots. Acta Horticulturae. 687: 235-242. 9. Herppich, W.B., S. Huyskens-Keil and R. Kadau (2005): Effects of short-term low-temperature storage on mechanical and chemical properties of white Asparagus cell walls. Journal of Applied Botany and Food Quality. 79: 63-71. 10. Huyskens-Keil, S., R. Kadau and W.B. Herppich, (2005): Textural properties and cell wall metabolism of white asparagus spears (Asparagus officinalis L.) during Postharvest. Acta Horticulturae. 682: 461-467. 11. Grszynska, D.M., B. Michalczuk and R.M. Rudnicki (1989): The effect of floral preservative enriched with calcium nitrate on keeping quality of cut ´Sonia` roses. Acta Horticulturae. 261: 281-286. 12. ASAE. (1999): Compression test of food materials of convex shape. ASAE Standarts, Standarts engineering practices data 46th ed.; ASAE, St. Joeph, MI, USA. 13. von Willert, D. J., R. Matyssek and W.B. Herppich (1995): Experimentelle Pflanzenökologie: Grundlagen und Anwendungen. Georg Thieme Verlag: Stuttgart. 14. Schmid, O., F. Steinbacher, S.Spinarova and L. Hendriks (2006): Transpirationsstudien an Schnittrosen im Nachernteprozess. Proceedings of the 43. Annual Meeting of the German Society of Horticultural Science, Potsdam, 22-25 February. 227.

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