Promotion of Radish Cotyledon Enlargement and Reducing Sugar Content by Zeatin and Red Light

Abstract

Effects of zeatin on amino acid and sugar contents of detached radish (Raphanus saivus L) cotyledons were investigated to determine if accumulation of these solutes contributes to cytokinin-enhanced growth. Protein (14,18,21), and certain portions of grass leaves expand faster after treatment with either of these stimuli, as evidenced by leaf unrolling (11,23). In light-sensitive lettuce seeds, cytokinins increase the growth rate of cotyledons (5), while red light primarily enhances elongation of radicle cells (20). Cotyledons from numerous other dicots also grow faster in the presence of exogenous cytokinins (2,4,9,10,16,19), and this phenomenon has been developed as a cytokinin bioassay by Esashi and Leopold (2), Letham (9,10), and Narain and Laloraya (16). ing wall plasticity, while red light-enhanced lettuce seed germination seems to arise from an osmotic effect due to more rapid degradation of some macromolecule (15). We are not aware of data indicating that either red light or cytokinins increase wall plasticity, and our studies were to determine whether increased cell expansion (10) of excised radish cotyledons by cytokinins could be due to water uptake resulting from osmotic effects of enhanced solute accumulation. We found that both cytokinins (in the presence of light) and red light increased the reducing sugar contents of the cotyledons, and these increases were highly correlated with cotyledon growth. MATRIAILS AND METHODSRadish seeds (Raphanus sativus L. var. Early Scarlet Globe) were surface sterilized with 10% (v/v) Clorox and, after thoroughly rinsing, were germinated in darkness for 48 hr on wet paper. The smaller cotyledon cut from each selected seedling was used in all studies. Usually five cotyledons (20-35 mg fresh weight) were randomly selected for each sample, blotted gently, weighed as a group, and placed adaxial side down on Whatman No. 1 filter paper covering the bottom of a 5.5-cm Petri dish. The filter paper was previously wetted with 1 ml of 2 mm potassium phosphate buffer (pH 6.4) containing designated additives. The Petri dishes were placed on wet paper towels in glass trays covered with clear plastic film, and cotyledons were incubated at 25 C. The trays were also covered with aluminum foil for incubation in darkness. After incubation, cotyledons were blotted and reweighed.Immediately after obtaining final weights, cotyledons in each sample to be analyzed for protein and amino acids were placed in 10 ml of hot 80% (v/v) ethanol and boiled until volumes were reduced to about 2 ml. An additional 10 ml of 80% ethanol was then added, and samples were homogenized with a Brinkmann Polytron and centrifuged for 15 min at 17,300g at 4 C. Supernatant volumes were adjusted to 20 ml, and a-amino nitrogen was determined on 1-ml aliquots, as described by Yemm and Cocking (24), using glutamine as a standard. Residues from centrifugation were prepared for protein analysis by twice dissolving in 0.1 N KOH and precipitating with 10% (w/v) trichloroacetic acid. The final precipitates were...

Water stress effects on the content of low molecular weight carbohydrates and phenolic acids in Ctenanthe setosa (Rosc.) Eichler

“…Sugars are known to be involved in normal osmotic adjustment (Huff and Ross 1975). Sugar accumulation has been implicated as a factor in increasing protoplasmic tolerance to water deficits (Lee-Stadelmann and Stadelmann 1976).…”

Solutes Contributing to Osmotic Adjustment in Cultured Plant Cells Adapted to Water Stress

“…Sugars are known to be involved in normal osmotic adjustment, i.e. those not associated with stress (16). Many of the other solutes seem to become more correlated to the 44,, changes associated with the cell growth cycle after substantial adaptation to stress, suggesting that increased regulation over their intracellular levels has occurred during adaptation.…”

“…to external^ti of - 16 (P20 line), -22 (P25 line), and -28 bar (P30 line), imposed by the addition of PEG (20%, 25%, and 30%, respectively) to medium (3, 1 1). These cell lines offer an excellent system for studying osmotic adjustment since they are virtually isogenic and have undergone different levels of osmotic adjustment (4).…”

Estimation of Osmotic Parameters Accompanying Zeatin-Induced Growth of Detached Cucumber Cotyledons

“…The most intensive investigations of this phenomenon have been performed with radish (1,3,6,13,18) and cucurbits (4,8,18). In these species, dry weight changes with or without cytokinin are negligible during growth periods of 3 d and, at least in radish (1,3), cytokinesis is increased by cytokinins much less than is H20 uptake.…”

“…In each species, cytokinins cause wall loosening that apparently contributes substantially to water uptake and thus growth promotion (16,18). Nevertheless, cytokinin-enhanced production (6,8) and absorption (4,13) All ' values were estimated by the gravimetric method of Ursprung (see Ref. 9).…”