Comparison of phosphorus mobilization during monocarpic senescence in rice cultivars with sequential and non-sequential leaf senescence

The senescence pattern of the three uppermost leaves of four rice (Oryza sativa L.) cultivars viz. Ratna, Jaya, Masuri and Kalojira was analysed in terms of decline of chlorophyll and by measuring [³²P]-phosphate retention and export from leaf to grains during the reproductive development. With the advancement of reproductive development, the cultivars Masuri and Kalojira showed a sequential mode of senescence, but the cultivars Ratna and Jaya showed a non-sequential mode of leaf senescence where the flag leaf senesced earlier than the older second leaf. Foliar spraying with benzyladenine (0.5 mM) significantly delayed, and abscisic acid (0.1 mM) accelerated, leaf senescence. In untreated control plants, the second leaf had the highest export of labelled phosphate among the leaves at the grain formation stage (0–7 days) in Masuri and Kalojira. This was compensated by the flag leaf at the grain development stage (7–14 days), whereas export of [³²P]-phosphate was highest from the flag leaf of Ratna and Jaya at the grain development stage. Compared with the control, benzyladenine treatment caused higher retention of [³²P]-phosphate in the leaves and also export to the grains, but abscisic acid treatment gave lower retention and export of [³²P]-phosphate to the grains. The amount of [³²P]-phosphate export from a mother to a daughter shoot developed in the axil of the second leaf of plants with the panicle removed, was less than that to panicles remaining on control plants of all cultivars. When the panicle had been excised, the greatest export of [³²P]-phosphate took place from the second leaf to the daughter shoot in all cultivars. Excision of the panicle delayed leaf senescence as compared with intact controls and maintained an age-related leaf senescence pattern in all the four cultivars. The results presented here demonstrate that mobilization of phosphorus from leaf to grains, regardless of cultivar or age and position of the leaf, correlates well with the senescence of that leaf.     

Hydrogen peroxide metabolism as an index of water stress tolerance in jute

Two species of jute plants Corchorus capsularis L. (cv. JRC 212) and C. olitorius L. (cv. JRO 632) were subjected to water stress for 2 and 4 days by withholding water. The relative water content (RWC) decreased in both plants under water stress but to a greater extent in C. olitorius . The C. olitorius seedlings also showed greater membrane injury than C. capsularis seedlings under water stress as was evident from injury index data. Water stress increased glycolate oxidase (EC 1.1.3.1.) activity more in C. olitorius than in C. capsularis . The activity of superoxide dismutase (SOD, EC 1.15.1.1.) and catalase (EC 1.11.1.6.) decreased under water stress and their decrease was higher in C. olitorius than in C capsularis . The level of hydrogen peroxide and lipid peroxidation also increased in both plants under water stress and the increase was higher in C. olitorius than in C. capsularis seedlings. Under comparable external water stress, C. capsularis seedlings showed lower membrane damage, lower H₂O₂ accumulation and lower lipid peroxidation than C. olilorius which may be taken as indicative of higher water stress tolerance capacity of the former.     

Effect of water stress at different developmental stages of field-grown rice

Water-stress for 10d at different developmental stages, affected relative water content and leaf water potential of plants. Subsequent rewatering removed these effects. Water stress lowered the contents of chlorophyll, protein, RNA and the activity of catalase, while it increased free proline accumulation and activities of protease, RNase and peroxidase. An overall improvement in biochemical parameters was achieved as soon as the stress was withdrawn by watering and this was reflected in subsequent developmental stages. Water-stress at the reproductive stages induced similar changes as in the vegetative stage but the removal of stress could not improve these parameters to the same extent as at the vegetative stage. In consequence, stress applied at the vegetative stage augmented yield parameters but when applied at the reproductive stage it significantly reduced the yield.     

Effect of calcium on water-stress-induced biochemical changes and yield of field-grown rice

Three different treatments by calcium (10²M), namely seed treatment, foliar spraying and their combination were applied on field-grown rice (Oryza sativa L. cv. Ratna) under both water stressed and non-stressed conditions in the course of plant development. The relative water content and leaf water potential decreased with increase in age of stressed and non-stressed plants. Pretreatment of seeds with Ca improved the water status of the plants most prominently at the vegetative stage but the effect gradually faded away with plant development. The foliar spraying by Ca was more effective in improving the water status of the plants at the reproductive stage. The combined Ca treatment significantly improved water status of the plants both at the vegetative and reproductive stages. The contents of chlorophyll and protein decreased and the activities of protease and RNase increased in the course of plant development in both non-stressed and even more in stressed plants. Ca treatments of seeds or plants or their combination inhibited the decline in chlorophyll and protein contents and the rising trends of protease and RNase activities, the combined treatment being most effective. During plant development free proline content increased significantly more in water stressed plants. In non-stressed plants there was a marked increase in the free proline content at the mature fruit stage. Ca treatment inhibited the rise of free proline in stressed plants. A significant reduction in yield components and yield of the crop in water stressed plants was increased by Ca treatment.     

Regulation of leaf senescence, grain-filling and yield of rice by kinetin and abscisic acid

Senescence of rice ( Oryza sativa L. cv. Jaya) leaves was regulated with kinetin and abscisic acid (ABA) sprays at the reproductive stage. The effect of such sprays on grain-filling and yield was analyzed. Spraying 100-day-old plants with kinetin solution (100 μg ml^-1) significantly delayed senescence as indicated by higher total chlorophyll and protein levels in the three uppermost leaves compared with the controls. In contrast, spraying with ABA (15 μg ml^-1) significantly promoted foliar senescence. The number of spikelets per panicle, number of panicles, percentage filled grains, panicle weight and grain yield per plant and the mobilization and harvest indices were significantly increased by kinetin treatment, while ABA decreased most of them. The possibility of increased grain-filling and thus, yield due to delayed foliar senescence by kinetin treatment and decreased grain-filling due to hastening of senescence by ABA is discussed.     

Changes in polyamines and related enzymes with loss of viability in rice seeds

Putrescine, spermidine and spermine of high vigour, low vigour and non-viable (classes 1, 2 and 3 respectively) seeds of Oryza sativa increased with loss of viability. The largest concentration of spermine was found in non-viable embryos. Spermine was absent in the husks of all the three categories of seeds. Arginine decarboxylase was greatest in high vigoured seeds and its activity gradually declined with loss of viability. However, diamine oxidase and polyamine oxidase activities gradually increased with the loss of viability of the seeds while DNA, RNA and protein contents decreased. The total content of polyamines increased on kinetin treatment but declined on ABA treatment. DNA, RNA and protein followed the same trend as polyamines. The polyamine contents increased by ca 3- and 4-fold, respectively, in high vigoured and low vigoured seeds on 10^?4 M kinetin treatment. The activity of ADC followed the same change as that of the polyamines in both cases, but the reverse was observed for the activities of diamine and polyamine oxidases.     

Changes occurring during aging and senescence in a submerged aquatic angiosperm (Potamogeton pectinatus)

Changes occurring during aging and senescence of leaves of a submerged aquatic angiosperm ( Potamogeton pectinatus L.) were studied. Total chlorophyll and chlorophylls a and b were maximal in mature, and minimal in old leaves. The chlorophyll a to b ratio was highest in mature leaves. During senescence, the chlorophyll content and the ratio of chlorophyll a to b decreased. The content of DNA, RNA, protein and dry weight, and the activity of alkaline pyrophosphatase decreased while free amino acids, the activity of protease, RNase and acid pyrophosphatase, and the ratio of acid to alkaline pyrophosphatase activity increased during aging and senescence. Kinetin (0.23 m M ) deferred leaf senescence by delaying the loss of chlorophyll, protein, nucleic acids and dry weight, and reducing the rise in free amino acids, the activity of protease, RNase and acid pyrophosphatase and the ratio of acid to alkaline pyrophosphatase activity; while both 0.69 m M ethrel and 0.075 m M ABA hastened senescence. Kinetin pretreatment for an optimum period (12 h) followed by ethrel or ABA treatment partially erased the senescence-promoting effect of the latter. But treatments in a reverse order markedly reduced the delaying effect of kinetin on senescence.     

Influence of reproductive organs on plant senescence in rice and wheat

The chlorophyll and protein contents of the flag, second and third leaves gradually decreased during the reproductive development of rice (Oryza sativa L. cv. Rasi) and wheat (Triticum aestivum L. cv. Sonalika) plants, whereas proline accumulation increased up to the grain maturation stage and slightly decreased thereafter. In rice plant, the rate of decrease in chlorophyll and protein and increase in proline level were higher in the flag leaf than in the second leaf. It was opposite in wheat plant. The export of [³²P]-phosphate from leaves to grains gradually increased reaching a maximal stage at the grain development stage, and then declined. The export of this radioisotope was greater in rice than in wheat. Removal of panicle at the anthesis and grainfilling stages delayed leaf senescence of rice plant, while in wheat the ponicle removal at any stage did not have a marked effect on delaying leaf senescence. The contents of chlorophyll and protein of glumes were higher in wheat than in rice. The variation of such source-sink relationship might be one of the possible reasons for the above effect on leaf senescence.     

Effect of water stress on some oxidative enzymes and senescence in Vigna seedlings

Seedlings of Vigna catjang Endl. were subjected to water stress for 6, S and 10 days by withholding water to investigate the activities of some oxidative enzymes and the pattern of senescence in leaves of 17-day-old seedlings undergoing water stress. Increasing duration of stress produced a proportional increase in the activities of IAA-oxidase, AA-oxidase, peroxidase and glycolate oxidase but decreased catalase activity and the contents of both chlorophyll and protein, hastening senescence. Leaf water potential and relative water content were also lowered with incresing duration of stress. Permeability was increased in leaf tissue undergoing water stress for 8 days. Seed treatment with CaCl₂ (10⁻² and 10⁻¹⁴ M ) for 6 h improved the water status of leaves, decreased tissue permeability, activities of oxidative enzymes, decline of chlorophyll and protein contents and delayed senescence compared to untreated water stressed plants.     

Genetic polymorphisms in GSTM1, GSTT1, GSTP1, GSTM3 and the susceptibility to gallbladder cancer in North India

Abstract

The glutathione S-transferase (GSTs) are polymorphic supergene family of detoxification enzymes that are involved in the metabolism of numerous potential carcinogens. Several allelic variants of polymorphic GSTs show impaired enzyme activity and are suspected to increase the susceptibility to various cancers. To find out the association of GST variants with risk of gallbladder cancer, the distribution of polymorphisms in the GST family of genes (GSTT1, GSTM1, GSTP1, and GSTM3) were studied in 106 cancer patients and 201 healthy controls. Genotypes were analysed by polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism (RFLP). The frequencies of GSTM1 null and GSTM3*BB genotypes did not differ between patients and controls. The overall frequency of GSTT1 null was lower in cases as compared with controls (p=0.003, Odds ratio (OR)?=?0.2, 95% confidence interval (CI), 0.1–0.6). After sex stratification, the GSTT1 null frequency was reduced only in female patients (p=0.008, OR?=?0.2, 95% CI?=?0.1–0.6). However, the GSTP1, ile/val genotype and the val allele were significantly higher in cases than controls (p=0.013, OR?=?1.9, 95% CI?=?1.1–3.1; p=0.027, OR?=?1.5, 95% CI?=?1.0–2.1), respectively. To study gene–gene interactions, a combined risk of gallbladder cancer due to ile/val or val/val were calculated in combination with null alleles of GSTM1 and GSTT1 or the *B allele of GSTM3, but there was no enhancement of risk. Gallstones were present in 57.5% of patients with gallbladder cancer, but there were no significant differences between allelic/genotype frequencies of the studied GST genes polymorphisms between patients with or without gallstones. To best of our knowledge, this is the first paper showing ile/val genotypes and val allele of GSTP1 to be associated with higher risk of gallbladder cancer.