Journal of the Japanese Society for Horticultural Science
Online ISSN : 1880-358X
Print ISSN : 0013-7626
ISSN-L : 0013-7626
Mechanism of the Thinning Action of NAA in kaki fruits
I. Relation between NAA-induced Fruit Abscission and Endogenous Growth Substances in Fruit Tissues
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1975 Volume 43 Issue 4 Pages 406-414


Changes in endogenous growth regulators shortly after the NAA application at 50 ppm about 20 days after full bloom were compared between large and small fruits of kaki"Fuyu". The size of the former was larger and that of the latter smaller than 2.21cm and 1.80cm in the cross diameter measured at the time of application, respectively.
1) Based on the three year′s experiments from 1970 to 1972, it was confirmed that NAA-induced fruit drop reached its peak 3 or 4 days after spraying and was nearly completed within another 4 days. A reverse relationship was found between fruit size of the application time and drop ratio; i. e., smaller fruits which usually contained fewer seeds were more sensitive to NAA than larger ones.
2) In either pericarp tissue including seeds of calyx tissue, higher activity of GA-like substances was detected in larger than in smaller fruits just prior to the application. Though their activity decreased in both large and small fruits in less than 3 days after application, the level of activity in large fruits was still higher than that of non-treated small fruits.
The auxin-type promoters contained in large and small fruits were different from each other in the chromatographic behavior. No distinctive change in the promoter content was caused in large fruits by the application of NAA though a drastic decrease of them occurred in the small fruits.
3) The level of ABA-like inhibitors was higher in small than in large fruits just prior to the application. Almost no change in inhibitor content was observed in large fruits even 3 days after the application, while the small fruits exhibited a remarkable increase of them during the same period.
4) The thinning action of NAA was negated almost completely by the supplementary treatments with GA3 or GA7 24 and 40 hours after the application.
5) Based on the above facts, it is possible to assume that NAA acts as a thinner against kaki through its effects on the levels of endogenous growth regulators in fruit tissues, resulting in the accerelation of physiological drop of relatively smaller fruits.

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