Effect of brief treatments with benzyladenine on growth and development of watermelon cotyledons

Abstract

Watermelon (Citrullus vulgaris Schrad.) cotyledons were excised from the seed after 24 h of imbibition and incubated for different times (ranging from 1 to 240 min) on filter paper saturated with 0.1 mM BA (benzyladenine) solution. After the incubation in BA the cotyledons were thoroughly rinsed in water and grown for 5 days in darkness on filter paper saturated with distilled water. Continuous presence of BA is not a prerequisite for optimal growth. Several effects of the hormone (stimulation of expansion growth, acceleration of lipid breakdown, enhancement of hydroxypyruvate reductase activity, increase in carotenoid content) are more intensive if the cotyledons are treated with BA for a relatively short time and then grown in water. Maximal effects are observed after a 4 h exposure to BA. A single 1 min exposure is sufficient to elicit measurable effects on growth, hydroxypyruvate reductase and carotenoid content. The sensitivity to very short exposures is considerably different for different hormone effects. Carotenoid content and hydroxypyruvate reductase activity are enhanced much more than expansion growth.

Uptake of Benzyladenine by Excised Watermelon Cotyledons

“…Earlier work done in our laboratory showed that treatments with lO-' M BA for as short as 1 min are sufficient to evoke longlasting responses in watermelon cotyledons (8). These results suggested that cotyledons are able to take up BA quite efficiently from the external medium.…”

“…of BA + derivatives) present in the cotyledons and the magnitude of hormonal responses that are observed four days after uptake. This relationship holds regardless of whether a given level of radioactivity has been reached after a short period of uptake or after a long period of uptake followed by washing.Although the action of exogenous cytokinins on excised plant organs is well documented (6,8,9) much less is known about their absorption. Studies on cytokinin uptake have been done with cultured cells (3) and with moss protonemata (5), but comparatively little work has been done with whole organs from higher plants (2, 10).…”

“…Although the action of exogenous cytokinins on excised plant organs is well documented (6,8,9) much less is known about their absorption. Studies on cytokinin uptake have been done with cultured cells (3) and with moss protonemata (5), but comparatively little work has been done with whole organs from higher plants (2,10).…”

“…Batches of 20 cotyledons were placed in a small Petri dish (50 mm diameter) containing one filter-paper disc imbibed with 1 ml 8-[4C]BA solution (1.34,Ci/,tmol) at l-4 M concentration. After an appropriate time of incubation in darkness at 27 C or 2 C the cotyledons were blotted dry, thoroughly rinsed with distilled H20 as described (8) and extracted in boiling 80%1o ethanol (v/v) for 1 h. For each uptake experiment we used 4 batches of 5 cotyledons that were extracted separately with 5 ml ethanol. One ml of the ethanol used for extraction was added to 10 ml Luma Gel in a scintillation vial.…”

Uptake and Effects of N6-Benzyladenine in Excised Watermelon Cotyledons

“…We have shown (6) that continuous exposure to BA is not required for maximal effect. A treatment of 1 to 4 h with 10-' M BA is optimal, whereas a treatment of a few minutes suffices for a significant response.…”