Activities of Enzymes of Carbohydrate Metabolism during Development of Okra [Abelmoschus esculentus (L.) Moench] Seed

Changes in activity levels of important enzymes of carbohydratemetabolism (and ß-amylases, sucrose synthetase, acidinvertase, acid phosphatase, glucose phosphate isomerase, aldolase,phosphofructokinase and pyruvate kinase) during seed developmentwere determined. Changes in the activities of these enzymesand their functional significance in developing seeds are described.A close correlation was found between the stage of maximum carbohydrateoxidation and the accumulation of reserve materials in the developingseeds. ¹Present address: School of Agriculture and Forestry, Universityof Melbourne, Parkvilie 3052, Victoria, Australia. ²Present address: School of Botany, University of Melbourne,Parkville 3052, Victoria, Australia. (Received October 8, 1982; Accepted January 10, 1983)     

Effect of gibberellins A3, A4+7 and A13 and of (−)-kaurene on flowering and extension growth of Impatiens balsamina under different photoperiods

Summary Gibberellins A₃, A₄₊₇ and A₁₃ and (–)-kaurene delay floral-bud initiation and flowering and decrease the number of floral-buds and flowers in Impatiens balsamina under 4-hr photoperiods. They do not have any marked effect under 8-hr photoperiods. Under 16- and 24-hr photoperiods they hasten floral-bud initiation and flowering and increase the number of flowers, the effect being greater under 16- than under 24-hr days and the order of effectiveness being GA₄₊₇>GA₃>GA₁₃>(–)-kaurene.While GA₃ and GA₄₊₇ promote extension growth, the effect being greater with the former, GA₁₃ and (–)-kaurene do not promote it under any photoperiod. The magnitude of stem elongation in different treatments prior to floral-bud initiation increases from 4- to 8-hr photoperiods but decreases under 16- and 24-hr periods, the effect being more under 24-hr although both 16-and 24-hr photoperiods are noninductive for flowering.     

Immunological evidence for accumulation of two high-molecular-weight (104 and 90 kDa) HSPs in response to different stresses in rice and in response to high temperature stress in diverse plant genera

Rice seedlings accumulate stainable amounts of the 104 and 90 kDa polypeptides in response to high temperature stress. We have purified and raised highly specific polyclonal antisera against both of these polypeptides. In western blotting experiments, we find that these proteins are accumulated to different extents in rice seedlings subjected to salinity (NaCl), water stress, low-temperature stress and exogenous abscisic acid application. These proteins also accumulated when rice seedlings grown in pots under natural conditions were subjected to water stress by withholding watering. Seedlings of Triticum aestivum, Sorghum bicolor, Pisum sativum, Zea mays, Brassica juncea and mycelium of Neurospora crassa showed accumulation of the immunological homologues of both the 104 and the 90 kDa polypeptides, in response to high-temperature stress. We have earlier shown that shoots of rice seedlings exposed to heat shock accumulate a 110 kDa polypeptide which is an immunological homologue of the yeast HSP 104 (Singla and Grover, Plant Mol Biol 22: 1177–1180, 1993). Employing anti-rice HSP 104 antibodies and anti-yeast HSP 104 antibodies together, we provide evidence that rice HSP 104 is different from the earlier characterized rice HSP 110.     

Effects of Guaianolide derivative I on fibre initiation and elongation in Gossypium arboreum L. in relation to adverse effects of cool temperature

Cotton ovules collected during late September with prevalent night cool temperature (15°C), cultured at 30°C/15°C i.e. cycling temperatures in Beasley and Ting medium had very few epidermal cells showing bulging. Supplementing cultures with guaianolide derivative I (E-13 methyldehydrocostus lactone) promoted fibre initiation. At—1 day preanthesis (DPA), IAA oxidase activity declined in guaianolide-treated cultures but increased during the elongation phase and was enhanced during the secondary wall thickening phase. However, o-diphenol oxidase activity was adversely affected during the fibre initiation phase. The activities of all the other enzymes studied viz. acid invertase, phenylalanine ammonia lyase, -glucosidase and IAA oxidase increased, except -galactosidase, during the later phase in comparison with the controls. The present study indicates that guaianolide derivative I triggers early initiation and promotes fibre elongation by regulatin o-diphenols and IAA-oxidation levels, which in turn check wall loosening. Considerable enhancement in the soluble acid invertase activity by this compound suggests its role in apoplastic sucrose hydrolysis, thereby preventing its accumulation.Abbreviations DPA days pre anthesis - DAC days after culturing - DAA days after anthesis     

The Journey from Two-Step to Multi-Step Phosphorelay Signaling Systems

BackgroundThe two-component signaling (TCS) system is an important signal transduction machinery in prokaryotes and eukaryotes, excluding animals, that uses a protein phosphorylation mechanism for signal transmission.ConclusionProkaryotes have a primitive type of TCS machinery, which mainly comprises a membrane-bound sensory histidine kinase (HK) and its cognate cytoplasmic response regulator (RR). Hence, it is sometimes referred to as two-step phosphorelay (TSP). Eukaryotes have more sophisticated signaling machinery, with an extra component - a histidine-containing phosphotransfer (HPT) protein that shuttles between HK and RR to communicate signal baggage. As a result, the TSP has evolved from a two-step phosphorelay (His–Asp) in simple prokaryotes to a multi-step phosphorelay (MSP) cascade (His–Asp–His–Asp) in complex eukaryotic organisms, such as plants, to mediate the signaling network. This molecular evolution is also reflected in the form of considerable structural modifications in the domain architecture of the individual components of the TCS system. In this review, we present TCS system''s evolutionary journey from the primitive TSP to advanced MSP type across the genera. This information will be highly useful in designing the future strategies of crop improvement based on the individual members of the TCS machinery.     

Fabrication of an amperometric d-amino acid biosensor based on nickel hexacyanoferrate polypyrrole hybrid film deposited on glassy carbon electrode

A nickel hexacyanoferrate polypyrrole film was synthesized through an electrochemical two-step methodology leading to a very stable and homogenous robust hybrid film. A highly sensitive, specific and rapid amperometric d-amino acid biosensor was constructed by immobilizing d-amino acid oxidase on this film deposited over the surface of a glassy carbon electrode. The modified electrode was characterized by scanning electron microscopy, electrochemical impedance spectroscopy and Fourier transform infrared spectrophotometry. The biosensor showed optimum response within 1 s, when operated at 50 mV s^?1 in 0.01 M Tris HCl buffer, pH 7.0 at 30 °C. The biosensor exhibited excellent sensitivity with a detection limit of 1.5 µM (S/N = 3) for d-amino acids and wider linear range, 20–500 µM. Analytical recovery of added d-alanine (5 and 10 mM) in serum samples was 98.00 and 98.80 %, respectively. Within-batch and between-batch coefficients of variation in serum samples were 1.36 and 2.77 %, respectively. The enzyme electrode was used more than 50 times over 2 months, when stored at 4 °C. The proposed modified electrode exhibited sufficient mechanical and electrochemical stability and high sensitivity compared to earlier electrochemical d-amino acid biosensors. Interference by ascorbic acid and uric acid, the main interfering species in the biological samples, was negligible.     

Putative osmosensor – OsHK3b – a histidine kinase protein from rice shows high structural conservation with its ortholog AtHK1 from Arabidopsis

Prokaryotes and eukaryotes respond to various environmental stimuli using the two-component system (TCS). Essentially, it consists of membrane-bound histidine kinase (HK) which senses the stimuli and further transfers the signal to the response regulator, which in turn, regulates expression of various target genes. Recently, sequence-based genome wide analysis has been carried out in Arabidopsis and rice to identify all the putative members of TCS family. One of the members of this family i.e. AtHK1, (a putative osmosensor, hybrid-type sensory histidine kinase) is known to interact with AtHPt1 (phosphotransfer proteins) in Arabidopsis. Based on predicted rice interactome network (PRIN), the ortholog of AtHK1 in rice, OsHK3b, was found to be interacting with OsHPt2. The analysis of amino acid sequence of AtHK1 showed the presence of transmitter domain (TD) and receiver domain (RD), while OsHK3b showed presence of three conserved domains namely CHASE (signaling domain), TD, and RD. In order to elaborate on structural details of functional domains of hybrid-type HK and phosphotransfer proteins in both these genera, we have modeled them using homology modeling approach. The structural motifs present in various functional domains of the orthologous proteins were found to be highly conserved. Binding analysis of the RD domain of these sensory proteins in Arabidopsis and rice revealed the role of various residues such as histidine in HPt protein which are essential for their interaction.