The function of calcium in plants

Application of kinetin and Ca2+ caused a striking synergistic increase in ethylene production by mung bean (Phaseolus aureus Roxb) hypocotyl segments. The effect of kinetin on Ca2+ uptake and of Ca'+ on the uptake and metabolism of kinetin in relation to their effect on ethylene production was studied. Tracer experiments showed that kinetin greatly increased the uptake of 4"Ca2' after 6 hours of incubation. Reciprocallv, Ca2+ stimulated the uptake of kinetin-8-14C and remarkably enhanced the metabolism of kinetin-8-14C into several polar metabolites. Consequently, the quantity of free kinetin-8-'4C remaining in Ca2+-treated segments was much less than in control segments. A possible mechanism accounting for the synergism between kinetin and calcium on ethylene production is discussed.We have previously reported a large synergistic increase in ethylene production by mung bean (Phaseoluts aureus Roxb) hypocotyl segments when kinetin and Ca2+ were applied (12). The amount of ethylene produced was dependent on the concentrations of kinetin and Ca2+ ion applied. Analysis of the synergistic effect of kinetin and Ca2+ on ethylene production required examination of the effect of kinetin on the uptake of Ca>2 and the reciprocal effect of Ca+ on the uptake and metabolism of kinetin. This paper describes the stimulatory effect of kinetin on Ca2+ uptake and of Ca>2 on kinetin uptake and metabolism. A possible mechanism accounting for the synergism between kinetin and Ca2+ ion on ethylene production is discussed. MATERIALS AND METHODSSeeds of mung bean (Phaseolus aureus Roxb) were grown in vermiculite for 3.5 days in darkness at 24 C. Segments 2 cm long were cut from hypocotyls at a point 1 cm below the hook, as previously described (11). Lots of 20 segments were incubated in 5 ml of a medium consisting of 50 mM potassium phosphate buffer (pH 6), 2% sucrose, and a given concentration of labeled and unlabeled kinetin or Ca2+, as indicated, in a 50-ml Erlenmeyer flask. A plastic centerwell containing 0.2 ml of 40% KOH was hung in the flask to absorb the CO2 evolved. The flasks were sealed with rubber serum caps and incubated in a shaker at 27 C in darkness.At the time intervals indicated, 1 -ml gas samples were 1 This work was supported by National Science Foundation Grant GB-33907X.withdrawn by hypodermic syringe, and ethylene was assayed with a gas chromatograph equipped with an alumina column and a flame ionization detector. The flask was then flushed with air and recapped for the next determination.For uptake studies, the hypocotyls incubated with 4"Ca'+ (104 /Ci, 41.5 ,umoles) were washed with five changes of distilled H20. The tissue was then ground in a glass homogenizer in 4 ml of 95% ethanol. The debris was pelleted by centrifugation and the supernatant was collected. The pellet was serially extracted with 2 ml of H20; 2 ml, 3 ml, and 5 ml of 10 mM HCl; and lastly with 5 ml of 0.5 mM EDTA. The radioactivity of the incubation medium, of each extract, and of the debris was determined with a liquid scintillation ...

Section: Discussionmentioning

confidence: 99%

Interaction of Kinetin and Calcium in Relation to Their Effect on Stimulation of Ethylene Production

Lau¹,

Yang²

1975

“…The possible participation of calcium in regulatory systems in plants may be inferred from the fact that calcium is widely known to play a major role in membrane structure and function (10). Its importance in the regulation of ion transport is well known (6,26).…”

Section: Discussionmentioning

confidence: 99%

Deferral of Leaf Senescence with Calcium

Poovaiah¹,

Leopold²

1973

169

In view of the possibility that senescence may be a consequence of the deterioration of membrane compartments in the cells of leaves, calcium was studied as a possible agent which might defer senescence. The senescence of corn leaf discs was deferred by added calcium, and the effect was additive to the cytokinin deferral of senescence. Likewise, the senescence of Rumex leaf discs was deferred by added calcium, and the effect was additive to the gibberellin deferral of senescence.Detailed experiments with corn leaf discs established that the increase in apparent free space associated with senescence was completely prevented by calcium. An increase in hydraulic permeability during senescence was likewise demonstrated, and this increase was deferred by calcium; calcium plus benzyladenine was even more effective. Each of the measured functions of leaf senescence (chlorophyll content, protein decrease, apparent free space increase, and hydraulic permeability increase) was suppressed by calcium, and the interpretation is offered that the effects are a consequence of the calcium function in maintaining cellular membranes.Since the discovery by Richmond and Lang (17) growth chamber (2000 ft-c, 16 hr daily) at a temperature close to 22 C. At 8 to 10 days, leaf discs measuring 1 cm in size were taken from the primary leaf with the aid of a cork borer. The discs were floated in 10 ml of test solution, 10 discs per Petri dish in darkness at 25 C for 3 to 5 days.For the Rumex assay (Rumex obtusifolius L.), following the procedure of Whyte and Luckwill (27), old leaves which were uniformly green were selected from matured plants in the greenhouse, and they were allowed to stand overnight at 25 C in the dark with petiole in water. Leaf discs (1 cm) were cut with a cork borer and randomized, and 10 discs were floated in each Petri dish containing 10 ml of solution to be tested in the darkroom at 25 C for 4 or 5 days. Chlorophyll was extracted in ethanol. Ten leaf discs were transferred to 10 ml of ethanol in a closed vial and allowed to stand overnight, and absorbance was read at 665 nm. Experiments were repeated 4 to 6 times.For protein measurement 20 leaf discs were ground in a mortar and pestle with phosphate buffer at pH 6.5 and centrifuged at 800g to discard cellular debris. Protein was precipitated from the supernatant with 10% trichloroacetic acid and centrifuged at 10,000g for 10 min. The precipitate was dissolved in 5 ml of 0.1 N NaOH, and a 0.1-ml aliquot was used for protein analysis by the method of Lowry et al. (12).Apparent free space was determined by the method of Epstein (5). Twelve leaf discs were blotted on a paper towel to remove solution adhering to the surface. To initiate the absorption, the leaf discs were transferred to a salt solution (1 mm KCl) containing a radioactively labeled ion . At the end of the absorption period (90 min), the solution containing the radioactively labeled ion was decanted, and the leaf discs were blotted on a paper towel. Some leaf discs were used to determine the ini...

“…3). A lower level of calcium may have been adequate in a nutrient solution containing all essential ions at a lower balanced level (10).…”

Section: Methodsmentioning

confidence: 99%

Calcium Deficiency of Dark-grown Seedlings of Phaseolus vulgaris L.

Helms

1971

Hypocotyl collapse in dark-grown seedlings of Phaseolus vulgaris cv. Pinto was due to calcium deficiency. There was no evidence of an associated pathogen. The number of seedlings with hypocotyl collapse decreased and the mean hypocotyl length increased when increasing levels of calcium (0-100 micrograms per gram) were supplied in an external nutrient solution to seedlings grown under sterile conditions.When seedlings were supplied with a complete nutrient solution, containing calcium at 100 micrograms per gram, but minus potassium, magnesium, sulfur, nitrogen, or phosphorus, occasional plants developed hypocotyl collapse symptoms; however, the lengths of hypocotyls varied little from those of controls grown in complete nutrient. When the calcium level in the deficient nutrient solutions was raised to 200 micrograms per gram, the number of plants with hypocotyl collapse was reduced markedly. With complete nutrient solution minus calcium, seedlings developed symptoms of calcium deficiency irrespective of seed size, i.e., irrespective of whether or not the seed contained a total calcium content that was low or relatively high.An increase in hypocotyl length in response to an external supply of calcium was obtained with five cultivars of Phaseolus vulgaris L. and with one of Soja max Piper. A similar response to calcium was obtained for epicotyl growth of a cultivar of Vicia faba L., but not for a cultivar of Pisum sativum L.When Phaseolus vulgaris L. cv. Pinto was grown in the dark at a constant temperature of 25 C in vermiculite moistened with distilled water, some seedlings developed necrosis of the hypocotyl and failed to emerge, whereas others developed a grey translucency of the hypocotyl soon after emergence and subsequently collapsed. The nature of the symptoms suggested that they could be due to damping off, a widespread pre-and postemergence seedling disease which is incited by several fungal organisms (8,16). It also was possible that the disease was due to a bacterial pathogen. However, data in this paper will show that the symptoms were caused by calcium deficiency.Several reports show that incidence of seedlings with symptoms resembling damping off can be reduced by treatment of soil or seed with calcium. Albrecht and Jenny (1) Dark-grown bean seedlings are used in many physiological and biochemical experiments, and it was unexpected that they should be affected by a nutritional deficiency. Generally, it is assumed that the cotyledons provide adequate nutrients to support growth for a number of days. Burstrbm (4) stated, for example, that hypocotyls employed in routine growth tests are amply supplied with calcium from their seed.Although wilting of petioles, peduncles, and stems is associated with calcium deficiency in some plants (9), the author is unaware of a previous report which shows that wilting of hypocotyls can result from calcium deficiency. This paper describes experiments designed to identify the cause of the hypocotyl collapse symptom in Pinto bean seedlings and to learn if it occ...