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Salinity is a major constraint for plant growth, development and yield worldwide. Evaluation of a large number of germplasms in salt-stressed environments may help identify superior salt-tolerant genotypes. The present study dissects the genetic diversity of 33 pearl millet genotypes (landraces and inbred lines) for salinity tolerance through in vitro screening at the seedling stage. Our results revealed a significant reduction in total biomass and shoot growth of the salt-sensitive genotypes upon exposure to 150 mM NaCl, in contrast to the tolerant genotypes showing better growth characteristics. A significant differential effect of salt treatment on morphological traits was observed by analysis of variance (ANOVA), confirming substantial genetic diversity among all genotypes for salt tolerance. The genotypes were clustered into three groups based on multiple stress indices. The genotypes were also evaluated using principal component analysis (PCA) to identify the key contributing traits for stress tolerance. Based on these results, a total of four contrasting genotypes were selected for further biochemical and molecular analysis. Physiological studies confirmed that salt tolerance might be due to the higher content of osmolytes and the activity of antioxidant enzymes. Similarly, gene expression profiling of catalase (CAT), glutamate dehydrogenase (GDH), glutathione reductase (GR), and nitrate reductase (NR) revealed a profound increase in NR and GDH transcript levels in the tolerant genotypes, suggesting their major role as reactive oxygen species (ROS) scavengers under salinity. The overall findings of this study could be utilized further for candidate gene mining through "omics" approaches, aiming toward development of salinity resilient crop plants.

State CoElege, East Lansing.That administration of exogenous thyroxine will reduce both thyroidal 1131 uptake(1) and output ( 2 ) suggests the possibility of measuring thyroid secretion rate indirectly by determining amount of thyroxine required to suppress turnover of 1131 by the thyroid. Indeed, Perry(3) reported that when rats are first given 1131, and different groups are then given graded doses of thyroxine, inhibition of thyroidal 1131 output during a 48-hour period is proportional to dosage of thyroxine administered. He proposed this as a thyroid assay met hod.In our research the response of the rat thyroid to dosages of thyroxine that were increased progressively at intervals in the same individuals, instead of varying dosages between groups, was explored. The procedure developed permits estimation of thyroid secretion rate in smaller groups of animals than required by earlier methods. I t also points to the possibility of estimating thyroid secretion rate of individual animals.Jdetkods. Adult albino rats obtained from Carworth Farms, were maintained on a diet consisting of yellow corn meal 140 g, ground whole wheat 100 g, whole milk powder 80 g, linseed oil meal 40 g, alfalfa leaf meaJ 24 g, brewer's yeast 12 g, and iodized salt 4 g. The rat laboratory was maintained at temperature of 74 t 1°F. In each experiment rats of only one sex and approximately same age and size were used. Each rat was injected intraperitoneally with 30-40 pc of carrier-free II3l as NaI. Forty-eight to 72 hours were allowed for fixation of 1131 by the thyroid and urinary elimination of excess isotope. External thyroid counts were taken at the end of this period and at appropriate intervals thereaft.er, at constant geometry, by use of heavy lead *Pu,blished with approval of Director of Mid. Agric. Exp. Sta. as journal paper No. 1710 N.S. t We are indebted to Carolyn Mayotte for technical assistance and to Dr. H. A. Henneman for suggestions.counting table similar to that described by Albert (4). Either a bismuth cathode gamma counting tube (RCL, Mark 1 Model 13) or a scin'tillation counter (Nuclear Instrument and Chemical Corp., Model DS-1) was used. Prior to counting, each rat was injected intraperitoneally with sodium pentobarbital (30 mg/ kg). In addition, ether was given by inhalation when necessary to effmt complete immobilization. Counts were read on a count rate meter (Nuclear, Model 1615-B) set at 270 level of counting error. In each case the thyroid region was centered over the 13 mm tapered opening in the counting table and the rat shifted about slightly until maximum counting rate was attained. Body background counts were taken over the epigastric region. Thyroid counts were corrected by one-half the body background plus the general background by formula established by Wolff(2) and also for physical decay. The _I I 6 0 : OO I 2 L-THYROXINE, y PER 100 gm RAT FIG. 1. Effect of progressively increasing doses of thyroxine in individual rats on retention of in their thyroids. b at Harvard Libraries on July 10, 2015 ebm.sagepub...

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