Response of senescing cotyledons of clusterbean to water stress in moderate and low light: Possible photoprotective role ofβ‐carotene

Abstract

Senescence of clusterbean (Cyamopsis tetragonoloba L.) cotyledons in moderate light (12 W m-2) brings about a loss in the pigments, enhanced lipid peroxidation and a decline in PS II photochemical activity without any loss either in Dl protein or in the level of beta-carotene. The senescence syndrome is aggravated in the cotyledons of water-stressed seedlings with an increase in thylakoid lipid peroxidation, a decline in the level of beta-carotene and a quantitative loss in the Dl protein. Loss of the protein, however, is arrested in the seedlings experiencing water stress at low light (3 W m-2) intensity that correlates with the stability in the level of beta-carotene and a slow rate of lipid peroxidation. Loss of the protein in moderate light is attributed to water-stress sensitized photoinhibitory damage. The data on changes in the components of xanthophyll cycle suggest the low activity of the cycle both during senescence and water stress. It is, therefore, concluded that beta-carotene may contribute to the assembly and stability of the Dl protein during senescence and water stress in clusterbean cotyledons.

Water stress-sensitized photoinhibition in senescing cotyledons of clusterbean: Changes in thylakoid structures and inactivation of photosystem 2

“…An enhanced content of free radicals and consequent lipid peroxidation during the stress treatment in MI may also be attributed to the stressinduced suppression of the scavenging potential of the chloroplasts. This notion is supported by a decreased level of β-carotene as reported previously in the clusterbean cotyledons under the same experimental conditions (Deo and Biswal 2001) and a decline in the activity of SOD observed in this study (Fig. 2).…”

“…Water stress was imposed by growing the seedlings in 3 % aqueous PEG-6000 solution under controlled conditions as described in Deo and Biswal (2001). Fig.…”

“…Pusa navbahar) seeds were surface sterilized with 30 % ethanol and kept under running water for 10 h. The imbibed seeds were germinated in dark in wet blotting papers. Healthy germinated seedlings were transplanted in perforated aluminium foils on glass Petri plates containing distilled water or 3 % aqueous polyethylene glycol (PEG-6000) solution and were allowed to grow in a temperature controlled room at 25±2 o C as described in Deo and Biswal (2001). Seedlings grown with distilled water under moderate irradiance of 12 W m -2 were termed as moderate irradiance (MI) control and those with PEG-induced water stress under the same irradiance as MI+W.…”

“…Senescing cotyledons of 11-15 d old seedlings were used for the experiment. This phase of cotyledon growth in clusterbean is characterized as senescing phase (Deo and Biswal 2001). Pigments were extracted with chilled 80 % acetone.…”

Effect on Biochemical Parameters of Cyanobacterium Anabaena Sp Under Lead Stress.

“…Carotenoid plays an important role in photoprotection of chlorophyll (Deo and Biswal, 2001) by quenching the triplet Chlorophyll and scavenging the singlet oxygen and other reactive oxygen species (ROS) (Choudhury and Behera, 2001). Edwin, 1997;Moreland, 1980;Bhuniaet al, 1991 suggested that the loss of carotenoid accumulation may be due to the inhibition of carotenoid biosynthesis pathway leading to chlorosis of the organism or may be due to degradation membrane component of the thylakoid (Allen, 1984).…”