Studies on Organogenesis from explants of Begonia Erythrophylla

Caulogenesis and rhizogenesis were studied in cultured explants of Begonia erythrophylla. The patterns of development were compared to each other and to explants cultured on non-organogenic media. Initially morphological and histological observations were carried out using both light and scanning electron microscopy. Shoots and roots were formed from cells of epidermal origin and were often associated with glandular hairs. Deposition of starch was correlated to organogenesis, with starch grains localized in the superficial layers of the explant, prior to the formation of meristematic regions. Once formed, meristematic regions showed high levels of enzymatic activity compared to the surrounding tissues. Media transfer experiments were conducted between root inducing medium (RIM) and shoot inducing medium (SIM), shoot inducing medium and a basal medium containing no growth regulators (BM), and RIM and BM. It was found that explants became determined for shoot production after 7 days, while they were determined for root production after 3 days on RIM before transfer to BM. Explants were found to be weakly canalized for rhizogenesis for the first 2 days after determination, thereafter they became strongly canalized. Explants were strongly canalized for caulogenesis once determined. Culture on BM prior to exposure to an organogenic medium resulted in the gradual loss of competence with time, but exposure for 2 days to either SIM or RIM resulted in explants becoming competent to respond to opposite inductive medium. Using one and two-dimensional gel electrophoresis, both unlabelled protein and protein labelled in vivo with [35S]-methionine were extracted from organogenic and non-organogenic explants. Silver-stained gels and fluorographs were analyzed to identify different sets of polypeptides associated with development in vitro. Overall the levels of 59 silver-stained and 29 labelled polypeptides were altered. It was shown that rhizogenesis and caulogenesis in petiole sections of B. erythrophylla are associated with both quantitative and qualitative changes in the expression of polypeptides. Most of these changes occur at, or after, the point of organ determination. Some of those associated with caulogenesis were also observed when leaf discs were cultured on SIM. Tissues of mature plants were examined for the presence of these polypeptides. The process of caulogenesis in petiole explants can be further divided by the use of chemical inhibitors of shoot formation. Additions of sorbitol, ribose, acetylsalicylic acid or tri-iodobenzoic acid to SIM, respectively, inhibits shoot formation without killing the explants. These inhibitors are only effective if explants are exposed prior to certain stages of development, after which they fail to inhibit shoot formation. The effects of these inhibitors on the pattern polypeptide changes associated with culture on SIM was determined

Response of Arabidopsis thaliana seedlings to lead exposure: effect of pre-treatment with sodium nitroprusside

Plants are regularly exposed to unfavorable conditions that impose stress. Lead (Pb), is one of the major pollutants in the environment that causes serious public health and environmental concerns. Increasing levels of lead could also have severe consequences for plants. Plants exposed to lead stress initiate signaling pathways, and make specific changes in their cell physiology and metabolism to avoid or tolerate the stress. However, mechanisms to reduce the effects of lead may vary from plant to plant, developmental stage, and culture medium. Nitric oxide is an important signaling molecule in plant development and defense responses. It has been shown to play a major role in plant responses to several abiotic stresses, such as heat, chilling, drought, salt, UV irradiation and ozone exposure. The objective of this study is to examine the physiological responses to Pb exposure of Arabidopsis thaliana seeds pre-treated with sodium nitroprusside (SNP), a nitric oxide donor. All experiments were carried out using 7-day-old seedlings in a laboratory environment. Pb contents were determined using a graphite furnace spectrometer. Antioxidant assays and reactive oxygen species were carried out using a microplate reader. A major finding is that Pb treatment resulted in increased oxidative stress, which was counteracted by SNP pre-treatment. This and other results obtained are discussed in relation to a strategy to tolerate Pb accumulation in plant cells

Phenotyping of mungbean (Vigna radiata L.) genotypes against salt stress and assessment of variability for yield and yield attributing traits

Salt tolerance is a complex polygenic trait that is genotype specific and tolerance can depend upon a plants developmental stage. To evaluate reproductive stage specific salt tolerance as well as investigate the inherent variability of mungbean (Vigna radiata L.) genotypes with respect to seed yields and yield-related traits, a pot culture experiment was conducted using 26 mungbean genotypes and exposure to salt stress (EC = 8.0 dS/m) applied at the reproductive stage, just before the opening of the first flowers. The experiment involved maintaining 100% field capacity for three weeks and used a randomized complete block design with three replicates. Data were collected, included days to maturity, plant height (cm), number of pod-bearing branches per plant, number of pods per plant, pod length (cm), number of seeds per pod, 100-seed weight (g) and seed yield per plant (g). Salt stress led to a significant (p<0.001) decrease in seed yield per plant, with yields of the genotypes BMX 11116, BMX 11176, BMX 11140, BMX 11111 and BMX 11163 being the least impacted by exposure to salt. Principal component analysis revealed that the first two components explained 63.5% of the total variation among the mungbean genotypes. Seed yield per plant showed a significant positive correlation with days to maturity, number of pod-bearing branches per plant, number of pods per plant, pod length (cm), number of seeds per pod, and 100-seed weight (g). Cluster analysis grouped the 26 genotypes into five distinct clusters, where the tolerant genotypes placed in cluster I. Based on their stress tolerance indices BARI Mung-6, BMX 11176, BMX 11116, and BMX 11140 were categorized as tolerant genotypes, were selected for further study under direct field conditions and are recommended for the genetic improvement of salt stress tolerance in mungbean

Potential determinants of salinity tolerance in rice (Oryza sativa L.) and modulation of tolerance by exogenous ascorbic acid application

Rice is a relatively salt-sensitive crop with the reproductive and seedling stages being the most sensitive. Two separate experiments were conducted to isolate potential determinants of salinity tolerance and to investigate the possibility of modulating salt tolerance by exogenous ascorbic acid (AsA) application. Rice plants were imposed to salinity (EC= 10.0 dS m-1) both at the seedling and reproductive phases of growth. Salinity at the seedling stage resulted a sharp decline in shoot and root growth related traits including leaf chlorophyll content, while hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels increased. Plants experienced with salinity at the reproductive phases of growth showed a significant reduction in yield attributing traits while the tissue levels of H2O2 increased. Exogenous AsA application reversed the negative impact of salt stress, modulating the root and shoots growth and yield related traits and lowering H2O2 and MDA levels. FL-478 was identified as the most tolerant genotype at the seedling stage, with Binadhan-10 being the most tolerant at the reproductive stage. Grain yield panicle-1 significantly and positively corrected with number of filled grains panicle-1, panicle length, plant height, and spikelet fertility, and negatively correlated with H2O2 levels. Stress tolerance indices clearly separated the tolerant and susceptible genotypes. A principal component analysis revealed that the first two components explained 87% of the total variation among the genotypes. Breeding efforts could therefore to undertake for developing salinity tolerance by manipulating endogenous AsA content in rice

Studies on Organogenesis from explants of Begonia Erythrophylla

Caulogenesis and rhizogenesis were studied in cultured explants of Begonia erythrophylla. The patterns of development were compared to each other and to explants cultured on non-organogenic media. Initially morphological and histological observations were carried out using both light and scanning electron microscopy. Shoots and roots were formed from cells of epidermal origin and were often associated with glandular hairs. Deposition of starch was correlated to organogenesis, with starch grains localized in the superficial layers of the explant, prior to the formation of meristematic regions. Once formed, meristematic regions showed high levels of enzymatic activity compared to the surrounding tissues. Media transfer experiments were conducted between root inducing medium (RIM) and shoot inducing medium (SIM), shoot inducing medium and a basal medium containing no growth regulators (BM), and RIM and BM. It was found that explants became determined for shoot production after 7 days, while they were determined for root production after 3 days on RIM before transfer to BM. Explants were found to be weakly canalized for rhizogenesis for the first 2 days after determination, thereafter they became strongly canalized. Explants were strongly canalized for caulogenesis once determined. Culture on BM prior to exposure to an organogenic medium resulted in the gradual loss of competence with time, but exposure for 2 days to either SIM or RIM resulted in explants becoming competent to respond to opposite inductive medium. Using one and two-dimensional gel electrophoresis, both unlabelled protein and protein labelled in vivo with [35S]-methionine were extracted from organogenic and non-organogenic explants. Silver-stained gels and fluorographs were analyzed to identify different sets of polypeptides associated with development in vitro. Overall the levels of 59 silver-stained and 29 labelled polypeptides were altered. It was shown that rhizogenesis and caulogenesis in petiole sections of B. erythrophylla are associated with both quantitative and qualitative changes in the expression of polypeptides. Most of these changes occur at, or after, the point of organ determination. Some of those associated with caulogenesis were also observed when leaf discs were cultured on SIM. Tissues of mature plants were examined for the presence of these polypeptides. The process of caulogenesis in petiole explants can be further divided by the use of chemical inhibitors of shoot formation. Additions of sorbitol, ribose, acetylsalicylic acid or tri-iodobenzoic acid to SIM, respectively, inhibits shoot formation without killing the explants. These inhibitors are only effective if explants are exposed prior to certain stages of development, after which they fail to inhibit shoot formation. The effects of these inhibitors on the pattern polypeptide changes associated with culture on SIM was determined