Rejuvenation of Ageing Bean Leaves under the Effect of Low‐Dose Stressors

Abstract

The effect of low concentrations of some stress-inducing compounds like Cd, Pb, Ni, and Ti salts and DCMU on the senescence of chloroplasts was investigated in detached primary leaves of bean. After the petioles of ageing leaves had developed roots, these low-dose stressors stimulated chlorophyll synthesis and photosynthetic activity, as compared to the control, thus causing rejuvenation in treated leaves. The amount of photosystem I (lowest in DCMU-treated leaves) and light-harvesting complex II increased, while that of photosystem II decreased or remained unchanged. Fluorescence induction parameters indicated unchanged electron transport (except for DCMU treatment). CO2 fixation and, in some cases, starch accumulation was stimulated. In parallel, the occurrence of large plastoglobuli seemed to decrease in plastids of heavy metal-treated leaves. A cytokinin bioassay of leaf extracts confirmed the cytokinin-mediated effect of low-dose stressors, as the slopes of Chl and cytokinin curves were similar during the rejuvenation process. It is assumed that these stressors generate non-specific alarm reactions, which involve changes in the hormonal balance by increasing the synthesis of cytokinins.

Structural and chemical study of callus formation from leaves of Rubia tinctorum

“…Higher starch content might be resulted by the high sucrose concentration of medium but similar transient starch accumulation was observed in planta too as a consequence of stress factors (Nyitrai et al 2004).…”

Cultivar variations in cadmium and lead accumulation and distribution among 30 wheat (Triticum aestivum L.) cultivars

“…It was proposed that Cd in large amounts could replace Zn as a factor favoring the growth of the Zn hyperaccumulator Thlaspi caerulescen (Liu et al 2008). Another possible mechanism for the stimulatory effect of heavy metals may be that metal ions can serve as activators of enzyme(s) in cytokinin metabolism, which accelerates the growth of plants (Nyitrai et al 2004). However, Tang et al (2009) assumed that the stimulatory response of plants to heavy metals may be a rare and extreme phenomenon of hormesis, and the physiological metabolisms of plants may respond differently to the heavy metals at the stimulatory and inhibitory dose range.…”

Variations in cadmium accumulation among Chinese cabbage cultivars and screening for Cd-safe cultivars

“…An impossible mechanism for the stimulatory effect of Cd may be that metal ions can serve as activators of enzyme(s) in cytokinin metabolism, which accelerates the growth of plants. It was reported that cytokinins can delay senescence while maintaining the chlorophyll and photosynthetic activity of leaf tissues [38] and can take part in the remediation of the effect of some low-dose heavy metals [39]. However, a sharp reduction in cytokinin content in wheat seedlings (Triticum durum) was observed within 2 h of supplying cadmium [40].…”