Deferral of Leaf Senescence with Calcium

Abstract

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...

Leaf Senescence Signaling: The Ca2+-Conducting Arabidopsis Cyclic Nucleotide Gated Channel2 Acts through Nitric Oxide to Repress Senescence Programming

“…The basis for this conjecture is as follows. (1) Prior studies (Poovaiah and Leopold, 1973;Chou and Kao, 1992;Corpas et al, 2004;Guo and Crawford, 2005;Mishina et al, 2007) discussed above suggest that both leaf Ca 2+ and NO repress leaf senescence. (2) High levels of SA and expression of PR1 are associated with treatments that reduce NO production in leaves and induce early senescence (Morris et al, 2000;Mishina et al, 2007;Ü lker, et al, 2007); SA level and PR1 expression are elevated in leaves of dnd1 plants (Yu et al, 1998).…”

“…Darkness treatment can induce senescence in detached leaves (Poovaiah and Leopold, 1973;Chou and Kao, 1992;Weaver and Amasino, 2001;Chrost et al, 2004;Guo and Crawford, 2005;Ü lker et al, 2007). Ca 2+ can delay the senescence of detached leaves (Poovaiah and Leopold, 1973) and leaf senescence induced by methyl jasmonate (Chou and Kao, 1992); the molecular events that mediate this effect of Ca 2+ are not well characterized at present.…”

“…Ca 2+ can delay the senescence of detached leaves (Poovaiah and Leopold, 1973) and leaf senescence induced by methyl jasmonate (Chou and Kao, 1992); the molecular events that mediate this effect of Ca 2+ are not well characterized at present.…”

Delay of Membrane Lipid Degradation by Calcium Treatment during Cabbage Leaf Senescence

“…Reduced membrane PL3 content during senescence is an indication of membrane breakdown, as shown for senescing carnation petals (8,22 (19), either by preharvest application (5) or by postharvest dip or vacuum infiltration (18). However, some references cited in the review paper by Ferguson (7) report acceleration of senescence.…”

Abscission of Phaseolus and Impatiens Explants

“…After aging for specific intervals from excision and irradiation, a 1-ml air sample was withdrawn from the bottle with a syringe and injected into the gas chromatograph. The identity of the ethylene peaks was verified using a mercuric perchlorate solution (27) (19,20). Irradiated and nonirradiated explants were incubated for 90 to 100 min in specific concentrations of sterile CaCl2 solutions, then placed in Petri dishes that were poured with 1% (w/v) agar containing the same respective concentrations of CaCl2.…”