Nasir S.A. Malik* and Peter J. Davies. Section of Genetics, Development and Physiology, Division of BiologicaI Sciences, Cornell University,. Ithaca, N.Y. 14853 ...
Planta (Bert.)129, 191--192 (1976)
P l ~ J H ~ 9 by Springer-Verlag 1976
SHORT COMMUNICATIONS The Effect of Fruit Development on the Growth Capacity of Apical Meristems Nasir S.A. Malik* and Peter J. Davies Section of Genetics, Development and Physiology, Division of BiologicaI Sciences, Cornell University, Ithaca, N.Y. 14853, USA
Summary. The effect of fruit development prior to ripening on the growth of both axillary buds and grafted young buds was examined in pea (Pisurn satirum L. var Alaska). While fruit development retards the growth of these apices it has no effect on their growth capacity or senescence as compared to deflowered plants.
Under optimal environmental conditions whole plant senescence is controlled by the genetic programming of the plant which limits the ultimate age to which a plant will grow in the absence of other impinging factors (Lockhart and Gottschall, 1961). Superimposed on this genetic control, however, are the senescence inducing effects of the flowers and the developing and maturing fruits, which have been shown to affect the senescence of leaves (Molisch, 1928; Leopold el al., 1959; Wareing and Seth, 1967), roots (Sitton et al., 1967) and apices (Lockhart and Gottschall, 1961 ; Malik and Berrie, 1975). As the apices control the growth potential of the plant their senescence is clearly of utmost importance. Malik and Berrie (1975) grafted young apices (to avoid the endogenous aging of the apex) on to older rootstocks and showed that death of even young grafted apices could be caused by allowing the growth and maturity of fruits on the rootstock. By contrast the entire plant could be kept alive for extended periods, beyond that of the life of the main apex of the plant, if fruits were removed and young apices continually grafted onto the rootstock. Fruit development and maturity clearly cause apical senescence prior to genetically controlled senescence.This could be due either to a nutritional imbal*
Current address. Pakistan Atomic Energy Centre, Tando Jam,
Sind, Pakistan.
ance, as originally suggested by Molisch (1928), or to hormonal control(s) emanating from the fruits or under their influence. The former has been shown to be incorrect with regard to leaf senescence by Leopold et al. (1959), but Malik and Berrie (1975) showed that leaf-senescence does not necessarily correlate directly with whole plant senescence. The work of Malik and Bcrrie (1975), descrit~ed above, indicated that apical senescence was caused by fruit maturity, possibly by some senescence factor emanating from the fruit. They did not, however, determine whether fruit development affected the growth capacity of the apex. We therefore undertook to investigate the role of fruit development on the growth capacity of the apex by examining whether early stages of fruit development would cause any reduction in growth or prior senescence of the apex as compared to defruited plants. As genetically controlled senescence might overshadow results obtained with the plant's own apices, young apices with a longer growing capacity were also grafted onto the older plants. Peas (Pisum sativurn L. var Alaska) were grown in 15 cm pots, filled with soil, peat and sand (1 : 1 : 1, v/v/v) mixture and fertilized with a complete nutrient, in a green house at 21 C day and 15 C night. Supplementary florescent lighting was used to provide an 18 hour photoperiod. Scions from young seedlings (with 6 visible nodes) were grafted onto rootstocks when the rootstock had just started flowering. Grafted rootstocks were then divided into two groups of 6 plants. In one group flower buds were removed immediately as they became visible whereas in the other group flowers were allowed to develop and fruits were removed prior to their maturity. Rootstocks in both groups were decapitated after the formation of four flowering nodes, but scions were allowed to grow until their apex senesced. The experiment was repeated twice. In experiments where the effect of fruit development on axillary branches was studied, all branches except one were removed as soon as they started growing. The plants were harvested when growth at all points on the plant had ceased.
Iris evident from Table 1 that fruit development does not have a significant effect on the growth of a young
192
N.S.A. Malik and P.J. Davies: Fruit Development and Apical Growth
Table 1. The effect of fruit development on the growth of branches developed from buds or scions, as measured by the length and total number of nodes formed at the time of harvest Treatment on main stem (or rootstock)
Axillary branch or scion
Flowers removed at Fruit removed after Flowers removed at Fruit removed after
axillary
early stage } complete fruit development early stage } complete fruit development
Scion
Total number of nodes with standard error
{ 9_+0.75 8 _+0.33 {9_+0.47 9 _+0.34
scion, or on an axillary branch, as indicated by node number, or on the length of axillary branches. A slight reduction was seen in the length of scion. It was observed that, in the presence of fruits, scions and the axillary buds do not show any appreciable growth until the fruits were filled and removed. Malik and Berrie (1975) have previously shown that once the fruits mature and ripen no further apical growth occurs because a senescence stimulus emanating from the fruits kills the apex. The slight reduction in length of scions compared to axillary buds may be caused by the unfavorable grafting condition caused by the developing fruits at the time of grafting. The delay in branch growth suggests that fruit development in Alaska peas has a growth supressing effect on apical meristems, which could be through nutritional pull, hormonal diversion, or by the production of growth retarding substances that move towards meristematic regions. These effects are, however, temporary and have little effect on the inherent growth ability of apical meristems, as the apices start growing soon after the effects of developing fruits are removed. While nutrient or hormone mobilizing effects of fruit development might be important in enhancing leaf senescence (Simon, 1967; Wareing and Seth, 1967) they are only of secondary importance in the control
Total length of the branch (cm) with standard error 23.46_+4.10 21.50 +_2.70 24.20 +_3.32 18.27 _+2.03
of whole plant senescence, having no effect on the growth capacity or death of the apical meristem.
References Leopold, A.C., Niedergang-Kamien, E., Janick, J. : Experimental modification of plant senescence. Plant Physiol. 34, 570-573 (1959) Lockhart, J.A., Gottschall, V. : Fruit induced and apical senescence in Pisum sativum L. Plant Physiol. 36, 389-398 (1961) Malik, N.S.A., Berrie, A.M.M. : Correlative effects of fruits and leaves in senescence of pea plants. Planta (Berl.) 124, 169-- 175 (1975) Molisch, H. : Die Lebensdauer der Pflanze. (1928) Translated into English by E.H. Fulling: The longevity of plants. New York: Translator 1938 Simon, E.W. : Types of leaf senescence. In : Aspects of the biology of aging. Symp. Soc. exp. Biol. 21, pp. 215-230. Ed. : Woolhouse, H.W. London: Cambridge Univ. Press 1967 Sitton, D., Itai, C., Kende, H. : Decreased cytokinin production in the roots as a factor in shoot senescence. Planta (Berl.) 73, 296-300 (1967) Wareing, P.F., Seth, A.K. : Aging and senescence in the whole plant. In: Aspects of the biology of aging. Syrup. Soc. exp. Biol. 21, pp. 543-558. Ed.: Woolhouse, H.W. London: Cambridge Univ. Press 1967
Received 10 October; accepted 28 October 1975
