The v subunit of Escherichia coli RNA polymerase, consisting of 90 amino acids, is present in stoichiometric amounts per molecule of core RNA polymerase (a 2 bb H ). The presence of v is necessary to restore denatured RNA polymerase in vitro to its fully functional form, and, in an v-less strain of E. coli, GroEL appears to substitute for v in the maturation of RNA polymerase. The X-ray structure of Thermus aquaticus core RNA polymerase suggests that two regions of v latch on to b H at its N-terminus and C-terminus. We show here that v binds only the intact b H subunit and not the b H N-terminal domain or b H C-terminal domain, implying that v binding requires both these regions of b H . We further show that v can prevent the aggregation of b H during its renaturation in vitro and that a V8-protease-resistant 52-amino-acidlong N-terminal domain of v is sufficient for binding and renaturation of b H . CD and functional assays show that this N-terminal fragment retains the structure of native v and is able to enhance the reconstitution of core RNA polymerase. Reconstitution of core RNA polymerase from its individual subunits proceeds according to the steps a 1 a 3 a 2 1 b 3 a 2 b 1 b H 3 a 2 bb H . It is shown here that v participates during the last stage of enzyme assembly when b H associates with the a 2 b subassembly.

An efficient in vitro screening method has been developed for mulberry ( Morus spp. ) to screen salinity-tolerant genotypes from a large population. Axillary buds from field-grown plants were cultured on MS medium containing five different concentrations (0.0%, 0.25%, 0.5%, 0.75% and 1.00%) of sodium chloride (NaCl) in order to study the shoot growth pattern. Rooting was also tested at four different concentrations of NaCl (0.0%, 0.1%, 0.2% and 0.3.%). NaCl has been found to inhibit the growth and development of mulberry shoots and roots in vitro. The survivability of the axillary buds of the genotypes tested was reduced from 83.7% for the controls to 6.1% in 1.0% NaCl. The average number of roots developed by the genotypes ranged from 11.9 (controls) to 0.2 (0.3% NaCl). Out of the 63 genotypes tested, only seven--Rotundiloba, English black, Kolitha-3, Berhampore-A, Kajli, BC(2)59 and C776--developed roots in 0.3% NaCl. Root growth was also reduced drastically from 1.8 cm for the controls to 0.1 cm in 0.3% NaCl. To test the reproducibility of the results in soil, five tolerant and two susceptible genotypes, identified in this in vitro study, were selected and tested under ex vitro conditions. The significant correlation coefficients obtained between the performances of these genotypes under both types of cultural conditions revealed that in vitro screening of mulberry through axillary bud culture is an easy and efficient method to identify salt-adapted genotypes within a limited space and time period.

Tea [Camellia sinensis (L.) O. Kuntze] is an aluminum (Al) hyperaccumulator plant and is commercially important due to its high content of antioxidants. Although Al induced growth is well-known for the plants growing in acid soil, yet the cause underlying the stimulatory effect of Al has not been fully understood. To investigate the possible role of Al in growth induction, we studied morphological, physiological as well as biochemical changes of tea plant under different Al concentrations (0-4,000 μM). In hydroponics, Al (15 μM), enhanced shoot and root growth, but at higher concentrations, it caused oxidative damage which culminated in a cascade of biochemical changes, Al content increased concurrently with the maturity of the leaf as well as stem tissues than their younger counterparts. Hematoxylin staining indicated that Al accumulation started after 6 h of exposure in the tips of young roots and accumulation was dose dependent. The physiological parameters such as pigments, photosynthetic rate, transpiration and stomatal conductance were declined due to Al toxicity. Alteration in activated oxygen metabolism was also evidenced by increasing lipid peroxidation, membrane injury, evolution of superoxide anions and accumulation of H(2)O(2). Contents of phenols initially exhibited an acceleration which gradually plummeted at higher levels whereas total sugar and starch contents decimated beyond 15 μM of Al concentration. Activities of antioxidant defense enzymes were increased with the elevated concentration of Al. Expression of citrate synthase gene was up-regulated in the mature leaves, young as well as old roots simultaneously with increased concentration of Al in those parts; indicating the formation of Al-citrate complex. These results cooperatively specified that Al concentration at lower level promoted growth but turned out to be a stressor at elevated stages indicating the sensitivity of the cultivar (T-78) to Al.