Of nine plant growth regulators (indoleacetic acid, 1-naphthalene acetic acid, gibberellic acid, giberellin 4/7, 6-benzylaminopurine, 6-furfurylaminopurine, abscisic acid, and 1-aminocyclopropane carboxylic acid) tested, only 6-benzylaminopurine and abscisic acid affected 14C-photosynthate unloading from excised seed coats of Phaseolus vulgaris L. Unloading, in the presence of KCl, was stimulated by 25 to 40%. Stimulation occurred immediately for 6-benzylaminopurine and for abscisic acid within 10 to 12 minutes of application.

http://www.plantphysiol.org/content/plantphysiol/80/3/635.full.pdf

Growth Regulators Have Rapid Effects on Photosynthate Unloading from Seed Coats of Phaseolus vulgaris L.

A new system has been developed to study hormone-directed transport in intact plants during parthenocarpic fruit set induced by gibberellins. Gibberellic acid (GA3) and gibberellin A1 (GA1) applied to unpollinated ovaries of pea (Pisum sativum L. cv. Alaska) promoted sucrose transport from the leaf to the site of hormone application. In vivo experiments showed an early (30 min) accumulation of [14C]-sucrose in ovaries of pea stimulated by gibberellins. This activation of sucrose transport appears to be mediated by gibberellins (GA1, GA3), increasing both loading of phloem with sucrose in the leaf (source) and sucrose unloading in the ovary (sink). The ability of pea tissue segments to take up sucrose in vitro was not affected by the hormonal treatment.

Hormone directed sucrose transport during fruit set induced by gibberellins in Pisum sativum

We examined the effects of seed formation andpara-chlorophenoxyacetic acid (p-CPA)treatment on the growth and endogenous indole acetic acid (IAA) content ofmuskmelon fruit. The growth of parthenocarpic muskmelon fruit induced by 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) declined 15 days after anthesis (DAA),resulting in smaller fruit than those pollinated at harvest.p-CPA improved the growth of parthenocarpic fruit thatweretreated between 10 and 25 DAA. Endogenous IAA levels in the seedsof artificially pollinated fruit were at their highest at 10 DAA,then decreased, and increased again after 30 to 45 DAA, whereas,the levels in the empty seeds of parthenocarpic fruit were significantly lowerthroughout development. Although endogenous IAA levels in the placenta ofpollinated fruit were lower than those in the seeds, the changing patterns werevery similar to those in the seeds. Endogenous IAA levels in the mesocarp ofpollinated fruit remained lower than those in the placenta throughout fruitgrowth, and the pattern of change was similar to that of the placenta. Levelsinthe seed, placenta and mesocarp of p-CPA-nontreatedparthenocarpic fruit stayed lower than those in pollinated fruit.p-CPA increased the levels of IAA in the seeds, placenta,and mesocarp of parthenocarpic fruit after the first treatment (10DAA) to 15 DAA, while those in the mesocarp increasedsignificantly after the second treatment (25 DAA), but did notincrease in empty seed and placenta.

p-CPA increases the endogenous IAA content of parthenocarpic muskmelon fruit

Research on hormone regulation of seeds and fruits has developed considerably over the last few years with, in the background, the aim of improving seed quality. Major projects have thus been launched, for example, concerning soybean in the USA. Several reviews have recently surveyed the evolution of hormone levels and their possible roles during maturation, in the case of gibberellins [22], cytokinins [40] or abscisic acid [5, 23]. After consideration of the possible mechanisms for regulation of hormone levels, attention will be focused on their role during fruit and seed development. In the majority of studies, conclusions are based on the simultaneous occurrence of peak values in hormone content and certain morphological and biochemical changes, or on the results of an application of growth regulators to intact plants. Karssen [21] has discussed the limitations of these experimental approaches. Nooden [28], in his presentation of an integration of soybean pod development and monocarpic senescence, has shown how difficult it is to interpret a study on a whole plant. However, recent anatomical, physiological, and biochemical research has furnished us with tools, which are indispensible for a better understanding of the levels at which different hormones act. Thus, new interest has recently been shown in storage proteins [19, 30]. The development of precise analytical techniques (immuno-assay, use of cDNA clones) has made it possible, in the case of a few species, to characterize their main storage proteins and to monitor the kinetics of their accumulation.

Phytohormones in Seed and Fruit Development

Studies were carried out to elucidate the effects of 4-CPA (4-chlorophenoxy acetic acid) on translocation and distribution of 14C-assimilates in fruits growth of tomato.The distribution pattern of 14C-assimilates from the leaves just above and just below the 1st inflorescence was changed by 4-CPA (15ppm) treatment. The accumulation of 14C-assimilates to the 1st inflorescence started earlier and increased rapidly. However, the magnitude of the effects to the distribution pattern was different according to the leaf position. The pattern from the leaf just below the 1st inflorescence was extremely affected by 4-CPA but not from the leaf just above the 1st inflorescence, because the role of leaf to 1st inflorescence is different. That is, the sympodial branching system and the degree of connection of vascular bundles affect the distribution pattern. These phenomena were also found in the various leaf positions in other experiments.From these results, it can be shown that 4-CPA is the activator of the sink or activates the sink earlier. However, it is probable that the increase in accumulation of assimilates to the inflorescence is not a direct effect of 4-CPA, because the effects sometimes do not appear by the fail of timming of 4-CPA treatment.It seems that the latant ability of the flower itself for development is fully brought out by the activation of the sink or the acceleration of accumulation of assimilates with 4-CPA treatment.

Effects of Growth Regulator 4-CPA on Translocation and Distribution of Photoassimilates in Fruiting Tomato Plants

Using excised fruit/shoot systems of pea (Pisum sativum L.), the effect of the 10-day-old (post anthesis) fruit (sink) on the translocation of 14C-sucrose applied to the stipule (source) was investigated. We also examined the influence of various growth regulators on the source-sink relationships using this system. Indole-3-yl-acetic acid (100 or 200 ppm), gibberellic acid (25-100 ppm) increased 14C-sucrose translocation into the growing fruit by about 13% and 22–29%, respectively. 2-chloroethyl phosphonic acid, 6-benzyladenine and 2-methyl-4-chlorophenoxyacetic acid also increased 14C-sucrose translocation into the fruit by about 11–26%, 11–23% and 24–37%, respectively. Elevated fruit 14C-sucrose levels found in other treatments include, methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (300 or 1000 ppm), 2,3,5-triiodobenzoic acid (100 and 300 ppm) and butanedioic acid mono-(2,2-dimethylhydrazide) (30-300 ppm) by about 34%, 39–52% and 7–13%, respectively.

N. R. Achhireddy

Papers

The development of Pisum sativum explant systems for studies concerning source‐sink activities