Changes in growth‐substance contents during growth of wheat grains

Abstract

Samples of developing wheat grains were extracted at weekly intervals from ear emergence until maturity and the growth substances estimated by bioassay. Immature grains contained two cytokinins; one was similar to zeatin and another, with more cytokinin activity, had different properties. Ovules contained only small amounts of growth substances but at the end of anthesis the grains had a maximum content of cytokinin. The gibberellin content increased until 3 wk after anthesis then decreased; their auxin content increased until 4 wk after anthesis but decreased as the grains ripened and lost fresh weight. The husks contained smaller amounts of growth substances than the grains they surrounded. Exudates from young stems contained cytokinins and these may originate in the roots and move to the ears through the stems. The auxin in the grains was identified as indole-3yl-acetic acid and may be derived from the phenols present reacting with tryptophan. I N T R O D U C T I O NThe yield of wheat is determined both by the size and the number of grains in the ears. Growth substances regulate the growth of individual plant organs and hence determine their relative growth rates and the distribution of photosynthates.Growth substances were extracted from developing wheat grains and the husks surrounding them, and were also collected in exudates from the stems, where they move in the transpiration stream from the roots to the ears. This paper describes changes assessed at weekly intervals in the auxin, gibberellin and cytokinin contents of grains from ear emergence until maturity. Tryptophan, a precursor of indole-3ylacetic acid (IAA), was also estimated in the extracts. M A T E R I A L S A N D M E T H O D SWheat (cv. Kloka) plants were grown either in a glasshouse or in the field. Samples of twelve ears were removed from main stems only, at weekly intervals from ear emergence until maturity. The results are the means of three field experiments in three consecutive years and of two glasshouse experiments.Extraction of plant tissues. Grains were removed from the ears, counted, weighed and killed by immersion in boiling 95% ethanol for I min. When cool, the grains were macerated in the ethanol, the macerate was filtered under low pressure and the cell debris washed twice with 80 % ethanol. The husks, surrounding the grains, were extracted similarly. 22-2

Nitrogen accumulation in the inferior spikelet of rice ear during ripening

“…(3) Plant hormones play an important role in determining the partitioning of nutrients among spikelets. Although it is well known that plant seeds contain a large amount of plant hormones and their levels were determined during spikelet development in some graminaceous plants including rice (Wheeler 1972;Osada et al 1973;Harris et al 1976;King 1976;Oritani and Yoshida 1976;Radley 1976Radley , 1978Bangerth et al 1985), it remains to be determined how plant hormones regulate the partitioning of nutrients among the spikelets.…”

Correlation of Xylem Sap Cytokinin Levels with Monocarpic Senescence in Soybean

“…Defruiting or deflowering appears to increase the levels of CK activity in root bleeding sap or xylem sap from a wide range of species (3,31,33). Depodding of soybean at full pod extension greatly increased the xylem sap levels of DZR (5x) and ZR (2x), while Z increased to a lesser degree.…”

Role of cytokinin in enhanced productivity of maize supplied with NH4 + and NO3 −

“…plants grown with both N forms increased floret and kernel numbers compared with NO 3 nutrition. Because endogenous cytokinins have been implicated in the regulation of tiller formation and survival in cereals (Michael and Beringer, 1980), and in the establishment of kernel sink capacity (Wheeler, 1972), cytokinin supply is one factor that could be related to enhanced reproductive development induced by NH 4 + NO 3 nutrition.…”