Seasonal Changes in Abscission Responses to Auxin in Debladed Petioles

The abscission of debladed petioles of various ages in Ervatamiaand Coleus has been followed throughout the year. In general,the retention times for the two species were found to be maximalin the summer and minimal in the winter months. In both speciesolder petioles tended to abscise earlier. The occurrences ofan auxin-inhibitable stage-I and an auxin-promotable stage-IIwere clearly established. The sensitivity to auxin in both stagesdeclined with increase in age, particularly in the two-nodeand three-node twigs of Ervatamia and in the four-node twigsof Coleus. The durations of stage-I and stage-II were foundto be characteristically different in different seasons. Ingeneral, stage-I lasted longer both in younger petioles andduring the summer months. Auxin sensitivity in both stages wasgreater in summer than in winter. Intermediate results wereobtained in the other two seasons. In both the species the auxin-promotablestage-II weakened with time, as shown by a smaller promotionwith delayed auxin application.     

Effects of Plant Growth Regulators on Grain-filling and Yield of Rice

Effects of three phytohormones (IAA₁, GA₃ and kinetin) on grain-fillingand the pattern of ³²P translocation from individual leavesto grains were studied at intervals of 7 days during the progressof reproductive development of rice (Oryza saliva L. cv. Jaya).The plants were sprayed with 100 µg ml^–1 aqueoussolutions of the hormones at 100 days, when the plants wereentering the reproductive stage. Kinetin produced a pronouncedeffect on grain-filling as well as on ³²P mobilization fromindividual leaf to grains and increased yield, possibly by increasingleaf longevity. GA₃ and IAA also increased the grain-fillingand ³²P mobilization significantly over control but the effectswere less marked than those of kinetin. Oryza sativa L., rice, grain yield, translocation, growth regulators, gibberellic acid, indol-3-yl acetic acid, kinetin     

Seasonal Changes in the Levels of Some Cellular Components in the Abscission Zone of Coleus Leaves of Different Ages

The present study with intact petioles of Coleus of varyingages suggests an involvement of the phenomenon of mobilizationwith the abscission process. There was a gradual increase inthe levels of chlorophyll and nucleic acids and also solublenitrogen compounds in the proximal tissues with the approachof abscission with a concomitant decrease of these substancesin the distal tissues. This increase of metabolites in the proximaltissues was clearer in petioles at the first node than at thefourth node suggesting a lesser degree of metabolic activityof the proximal tissues in older petioles. The change of levelsof chlorophyll and nucleic acids and also of soluble nitrogenwas more marked in winter than in summer months. The application of NAA to petioles of the third node; just afterdeblading (i.e. in the auxin-inhibited stage 1), not only stoppedthe decline of nucleic acid levels (particularly RNA) at thedistal tissues but also caused an increase of nucleic acidsover the initial levels. This effect was more pronounced insummer than in winter months. If the initially inhibitory concentration of NAA was appliedin the auxin-promoted stage 2 of abscission, instead of an increase,there followed a quicker rate of decrease in nucleic acids (particularlyRNA). This effect was also more prominent in summer.