Pratap Kumar Pati

Auxin: a master regulator in plant root development

The demand for increased crop productivity and the predicted challenges related to plant survival under adverse environmental conditions have renewed the interest in research in root biology. Various physiological and genetic studies have provided ample evidence in support of the role of plant growth regulators in root development. The biosynthesis and transport of auxin and its signaling play a crucial role in controlling root growth and development. The univocal role of auxin in root development has established it as a master regulator. Other plant hormones, such as cytokinins, brassinosteroids, ethylene, abscisic acid, gibberellins, jasmonic acid, polyamines and strigolactones interact either synergistically or antagonistically with auxin to trigger cascades of events leading to root morphogenesis and development. In recent years, the availability of biological resources, development of modern tools and experimental approaches have led to the advancement of knowledge in root development. Research in the areas of hormone signal perception, understanding network of events involved in hormone action and the transport of plant hormones has added a new dimension to root biology. The present review highlights some of the important conceptual developments in the interplay of auxin and other plant hormones and associated downstream events affecting root development.

Exogenous application of brassinosteroid offers tolerance to salinity by altering stress responses in rice variety Pusa Basmati-1

Plant steroidal hormones, brassinosteroids, play a pivotal role in variety of plant developmental processes and adaptation to various environmental stresses. The present work investigates the response of various stress markers upon exogenous application of 24-epibrassinolide (EBL) on Pusa Basmati-1, a commercially important rice variety, under salt stress conditions. Rice seeds after treatment with different concentrations of NaCl alone or in combination with different concentrations of 24-epibrassinolide (EBL) were analysed for various growth parameters, protein, proline and malondialdehyde content (MDA) and antioxidant enzymes activities. The seedlings exposed to NaCl exhibited a significant decline in growth parameters and changes in the levels of antioxidant enzymes, however, treatment with EBL showed an improvement in growth, levels of protein and proline content and antioxidant enzymes activity. The enhanced levels of MDA content during salt stress in rice seedlings was decreased with EBL treatment. Further, the treatment with EBL increased the expression of various oxidative stress marker genes, although to different levels. Expression of various brassinosteroids (OsBRI1, OsDWF4) and salt (SalT) responsive genes, revealed the down regulation of OsDWF4 with application of EBL and upregulation of SalT in presence of salt stress thereby confirming the efficacy of the treatments. Interestingly, a significant down regulation of SalT gene was observed on application of EBL along with salt compared to salt treatment alone. On the other hand, the application of EBL alone and in combination with salt has resulted in upregulation of OsBRI1.

Versatile roles of plant NADPH oxidases and emerging concepts.

NADPH oxidase (NOX) is a key player in the network of reactive oxygen species (ROS) producing enzymes. It catalyzes the production of superoxide (O2(-)), that in turn regulates a wide range of biological functions in a broad range of organisms. Plant Noxes are known as respiratory burst oxidase homologs (Rbohs) and are homologs of catalytic subunit of mammalian phagocyte gp91(phox). They are unique among other ROS producing mechanisms in plants as they integrate different signal transduction pathways in plants. In recent years, there has been addition of knowledge on various aspects related to its structure, regulatory components and associated mechanisms, and its plethora of biological functions. This update highlights some of the recent developments in the field with particular reference to important members of the plant kingdom.

Versatile roles of brassinosteroid in plants in the context of its homoeostasis, signaling and crosstalks.

Brassinosteroids (BRs) are a class of steroidal plant hormones that play diverse roles in plant growth and developmental processes. Recently, the easy availability of biological resources, and development of new molecular tools and approaches have provided the required impetus for deeper understanding of the processes involved in BRs biosynthesis, transport, signaling and degradation pathways. From recent studies it is also evident that BRs interact with other phytohormones such as auxin, cytokinin, ethylene, gibberellin, jasmonic acid, abscisic acid, salicylic acid and polyamine in regulating wide range of physiological and developmental processes in plants. The inputs from these studies are now being linked to the versatile roles of BRs. The present review highlights the conceptual development with regard to BR homeostasis, signaling and its crosstalk with other phytohormones. This information will assist in developing predictive models to modulate various useful traits in plants and address current challenges in agriculture.

Effect of 28-homobrassinolide on antioxidant defence system in Raphanus sativus L. under chromium toxicity

Heavy metals have emerged as major environmental contaminants due to rapid industrialization and urbanization. The genotoxic, mutagenic and carcinogenic effects of heavy metal like chromium (Cr) on man, animals and plants have been documented. In plants, accumulation of heavy metals beyond critical levels generates oxidative stress. This stress is generally overcome by antioxidant defence system and stress shielding phytohormones. Thus, the present study has been focused to analyze the effect of one of imperative group of plant hormones, i.e., brassinosteroids (BRs) which have been reported for its protective properties for wide array of environmental stresses. Raphanus sativus L. (Pusa Chetaki) seeds pre-treated with different concentrations of 28-homobrassinolide (28-HBL) were raised under various concentrations of Cr(VI). It was observed that 28-HBL treatment considerably reduced the impact of Cr-stress on seedlings which was evinced upon analysis of morphological and biochemical parameters of 7-days old radish seedlings. The toxic effects of Cr in terms of reduced growth, lowered contents of chlorophyll (Chl), protein, proline; increased malondialdehyde (MDA) content and elevated metal uptake were ameliorated by applications of 28-HBL. Also, the activities of all the antioxidant enzymes except guaiacol peroxidase (POD), increased significantly when subjected to Cr stress in combination with 28-HBL. Overall, seed pre-soaking treatment of 28-HBL at 10−7 M was most effective in ameliorating Cr stress. The present work emphasizes the protective role of 28-HBL on regulation of antioxidant enzymes and its possible link in amelioration of stress in plants.

Studies on leaf spot disease of Withania somnifera and its impact on secondary metabolites

During an investigation of the disease profile of Withania somnifera, it was observed that leaf spot is the most prevalent disease. Repeated isolations from infected leaf tissues and pathogenicity tests showed the association of fungal pathogen identified as Alternaria alternata (Fr.) Keissler. Scanning electron microscopy showed various histological changes in the leaf tissues of infected plants. A decrease in total content of reducing sugars (20%) and chlorophyll (26.5%) was observed in diseased leaves whereas an increase was noticed in proline (25%), free amino acids (3%) and proteins (74.3%). High performance thin layer chromatography (HPTLC) analysis of secondary metabolites viz. withanolides, withaferin-A and total alkaloids of the diseased leaves vis-à-vis control revealed reduction in withaferin-A and withanolides contents by 15.4% and 76.3% respectively, in contrast to an increase in total alkaloids by 49.3%, information hitherto unreported in W. somnifera.

Effect of 24-epibrassinolide on oxidative stress markers induced by nickel-ion in Raphanus sativus L.

The present study illustrates the effect of 24-epibrassinolide (24-EBL) on morphological and biochemical parameters in radish (Raphanus sativus L.) seedlings grown under nickel (Ni) ion stress. The radish seeds pre-soaked in different concentrations of 24-EBL were sown in petridishes containing various concentrations of heavy metal (Ni).Observations were made on root/shoot length, fresh biomass, activities of antioxidant enzymes (ascorbate peroxidase, superoxide dismutase, catalase, monodehydroascorbate reductase, dehydroascorbate reductase, guaiacol peroxidase and glutathione reductase), lipid peroxidation, proline and protein content in 7-day-old Ni-stressed radish seedlings. Results indicate that seeds presoaked with 24-EBL reduced the impact of Ni-stress which was evident by assessing the morphological parameters, protein content and antioxidant enzyme activities. It was also observed that 24-EBL reduced the toxicity of heavy metal by influencing proline and malondialdehyde (MDA) content. The present study lays a foundation for understanding the role of 24-EBL in heavy metal stress amelioration, particularly in food crop. Analysis of behaviour of antioxidant enzymes will play a critical role in understanding the stress networking, further filling the knowledge gap on the subject.

DIRECT SHOOT REGENERATION FROM LEAF EXPLANTS OF ROSA DAMASCENA MILL.

SummaryA protocol for in vitro propagation using direct induction of shoot buds from leaf explants of in vitro-raised shoots of Rosa damascena var. Jwala is reported. The present study is the first report on direct shoot regeneration in scented roses. Elite plants raised from nodal explants and maintained for over 2yr in vitro on a static liquid shoot multiplication Murashige and Skoog (MS) medium supplemented with 5.0 μM benzyladenine (BA) and 3% sucrose were used. Petioles from fully developed young leaves, obtained after 4 wk of pruning of old shoots, were found to be ideal for regeneration of shoots. Initially the explants were cultured in an induction medium [half-strength MS+3% sucrose+6.8μM thidiazuron+0.27 μM α-naphthaleneacetic acid (NAA)+17.7 μM AgNO3] and subsequently transferred to the regeneration medium (MS+2.25 μM BA+0.054 μM NAA) after 7, 14, 21, 28, and 35d. The highest shoot regeneration response (69%) was recorded when shoots were kept in the induction medium for 21 d and later transferred to regeneration medium. Histological studies revealed direct formation of shoot buds without the intervening callus phase. In vitro rooting of micro-shoots was accomplished within 2wk on half-strength MS liquid medium supplemented with 10.0 μM IBA and 3% sucrose for 1 wk in the dark and later transferred to hormone-free medium and kept in the light. Plantlets, remaining in the latter medium for 5–6 wk when transferred to soil, showed 90% survival.

Exogenous Application of 28-Homobrassinolide Modulates the Dynamics of Salt and Pesticides Induced Stress Responses in an Elite Rice Variety Pusa Basmati-1

Brassinosteroids play an essential role in regulating various aspects of plant growth and development as well as adaptation to various environmental stresses. The present work provides an analysis of the response of various stress markers upon exogenous application of 28-homobrassinolide (HBL) on Pusa Basmati-1, a commercially important rice variety, under salt and pesticide (Chlorpyrifos and Imidacloprid) stress. Rice seeds treated with HBL were analyzed for various growth parameters, protein, proline and malondialdehyde content (MDA), antioxidant enzyme activities, and their gene expression analysis (Cu/Zn-SOD, Fe-SOD, Mn-SOD, APX, CAT, and GR) in the presence or absence of salt and pesticide stress. Stress-induced reduction in growth, protein, and chlorophyll content and enhancement of proline and MDA content of seedlings was observed. The exogenous application of HBL resulted in the improvement of growth parameters as well as protein and proline content. MDA content decreased significantly under the effect of HBL treatment both under stress and control conditions. HBL treatment also enhanced the activity of various antioxidant enzymes which corroborated with the reduced accumulation of O2⋅- and H2O2 under the effect of salt and pesticides. The differential response of various isoforms of SOD under the effect of HBL and stress treatments was observed under salt and among different pesticide treatments. From this study, the potent activity of HBL in stress mitigation in response to salt and pesticide treatment in rice is established.

Mitigation of adverse effects of chlorpyrifos by 24-epibrassinolide and analysis of stress markers in a rice variety Pusa Basmati-1.

The present paper first time reports the role of 24-epibrassinolide (EBL) in mitigating the adverse effects of Chlorpyrifos (CPF), a broad spectrum organophosphate insecticide by regulating the antioxidant defence system in an elite indica rice variety Pusa Basmati-1. It investigates the effect of CPF (0.02%, 0.04% and 0.06%) and EBL (10(-11), 10(-9) and 10(-7)M) treatments alone and in combination on rice seedlings. Various growth parameters, protein, proline and malondialdehyde (MDA) content and activities of antioxidant enzymes of seedlings were analysed. CPF showed an adverse effect on growth and protein content of seedlings whereas it leads to an enhancement in the level of MDA and proline content. The activities of antioxidant enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), guaiacol peroxidase (GPX) and monodehydroascorbate reductase (MDHAR) increased after treatment with CPF. Application of different concentrations of EBL along with CPF resulted in an overall improvement in the growth, level of protein and proline content and in the activity of various antioxidant enzymes whereas a decline in the levels of MDA content was observed. The work also investigated the changes at the transcript level of some key antioxidant enzymes like Cu/Zn-SOD, Fe-SOD, Mn-SOD, APX, CAT and GR. The expression of most of the genes was enhanced in response to CPF treatment. Application of EBL in conjunction with CPF resulted in a distinct enhancement in the transcript accumulation of Fe-SOD and CAT showing their important role in EBL mediated amelioration of CPF induced stress.