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The purpose of this study was to determine the agro-morphological, physiological, and transcriptional characteristics of ethyl methane sulfonate (EMS)-mutagenized M3alfalfa (Medicago sativaL.) mutants grown for 24 days under water deficit conditions following the first cutting at the blooming bud stage. Drought stress generally reduced all agro-morphological parameters measured. Cutting stress significantly reduced total chlorophyll contents of all genotypes, with the exception of mutant X20. Significant changes occurred in the levels of ascorbate peroxidase (APX), lipid peroxidation (TBARS), glutathione reductase (GR), superoxide dismutase (SOD) and crude protein levels. Drought stress considerably elevated GR levels in irrigated control (C1) and unirrigated control (C2) plants. In contrast to the other genotypes studied, mutant X20’s crude protein level increased significantly after the first cutting under 24 days of water deficit conditions, compared to the level found before cutting. The expression profiles of Medicago truncatula Response to Desiccation 2(MtRD2) and Medicago sativaproline dehydrogenase (MsProDH) genes differed based on the plant genotype and duration of drought stress. Drought stress increased MsProDHgene expression in X20, X50, and C2 plants by 4.57, 14.8, and 20.65 times, respectively. The findings of the expression study indicated that the MtRD2gene may play a key role in stress reduction rather than drought stress per se. The results of this study revealed that cutting and drought are two independent stress variables that should be evaluated separately when evaluating genotype response to both irrigated and unirrigated growing environments in alfalfa.

The effects of stratification and priming on germination and emergence performance of narrow-leafed purple coneflower (Echinacea angustifolia) seeds were investigated. Seeds were pre-chilled for 3 weeks at 4 ± 0.5 °C (39.2 ± 0.9 °F) in light or primed for 3 days at 20 ± 0.5 °C (68.0 ± 0.9 °F) in darkness in Nas and Read medium (NRM) or in 2% potassium nitrate (KNO3) supplemented with 3 or 5 μM 1-aminocyclopropane carboxylic acid (ACC) or 500 mg·L-1 (ppm) or 1000 mg·L-1 gibberellic acid (GA3). Following stratification and priming, seeds were subjected to germination and emergence tests at 25 ± 0.5 °C (77.0 ± 0.9 °F). Priming the seeds in NRM or KNO3 containing 3 μM ACC gave the highest germination percentages with 78% and 80%, respectively. Stratification alone increased germination to 69% compared to nontreated seeds, which had the lowest germination percentage of 57%. Emergence was enhanced by priming seeds in the presence of 3 μM ACC (75%) compared to stratified seeds (62%), while nontreated seeds had the lowest emergence percentage of 26%. These results indicate that priming in the presence of ACC might be an alternative to lengthy stratification treatments to break the dormancy and improve the germination and emergence of narrow-leafed purple coneflower seeds. [ABSTRACT FROM AUTHOR]

A screen for Arabidopsis mutants that were insensitive to methyl jasmonate (MeJA) in an assay for seedling root growth yielded only alleles of previously isolated mutants jar1 and coi1, with one exception. Mapping of the locus and morphological characterization of the new mutant suggested it might be allelic to axr1, which had not previously been reported to show resistance to MeJA. The F(1) from a cross of the new mutant with axr1-3 did not show complementation, confirming that these are the same genes. The new allele is called axr1-24. In addition to MeJA and indole-3-acetic acid (IAA), axr1-24 had decreased sensitivity to 1-aminocyclopropane-1-carboxylic acid, 6-benzylamino-purine, epi-brassinolide, and abscisic acid. Both axr1-24 and the previously characterized axr1-3 allele were shown to be susceptible to the opportunistic pathogen Pythium irregulare, a trait found in other jasmonate response mutants, including jar1-1. The double mutant jar1-1/axr1-3 was more resistant to inhibition of root growth by MeJA and was more susceptible to P. irregulare infection than either single mutant, suggesting these genes might act in independent response pathways. In contrast, resistance to IAA in the double mutant was not different from axr1-3. Northern-blot analysis showed that IAA induced the jasmonate-responsive lipoxygenase 2, AOS, and AtVSP gene transcripts and induction was strongly impaired in axr1-3. However, transcript induction by MeJA was only minimally affected in axr1-3. This study demonstrates that in addition to auxin signaling, the AXR1 locus is involved in MeJA response, providing a mechanistic link between jasmonate and auxin-signaling pathways.

Genetic improvement of sorghum [Sorghum bicolor(L.) Moench] for germination and seedling growth in cold conditions would permit earlier seeding, with a number of benefits. Field evaluation of germination and seedling cold tolerance, while ultimately necessary, is subject to unpredictable weather and limited to one period of the year. The objective of this study was to develop simple and reliable techniques capable of handling large numbers of genotypes, for estimating germination and seedling cold tolerance of sorghum in controlled environment, before field tests, and to compare results with seedling emergence in the field at low soil temperatures. Rate of germination, final germination percentage, and the rate of early shoot growth were evaluated as estimators of cold tolerance using 12 diverse genotypes and their test crosses. The largest difference among genotypes under both normal [25–30°C (day) and 20–25°C (night)] and cold stress conditions (constant 15°C) was shown by the rate of germination in petri dishes and of shoot growth in vertical plexiglass plates in normal conditions only. Rate of germination under controlled cold conditions was strongly correlated (P< 0.01) with rate of emergence in a field experiment seeded early in cold soil. This work indicated that the use of two tests under controlled conditions, (i) measuring shoot growth rate under normal temperatures followed by (ii) rate of germination at 15°C, and recording data at optimum times will greatly assist in efficiently screening genotypes for cold tolerance before final evaluation in the field.

Early planting of sorghum [Sorghum bicolor(L.) Moench] hybrids in temperate agriculture confers numerous advantages but requires genetic variation, both in lines and in parental effects for germination and seedling tolerance to low soil temperatures. The objectives of this study were to examine genetic variation among 12 diverse sorghum lines and their hybrids with two testers for their relative ability to germinate and emerge at low soil temperatures. Rate of germination, final germination level, and rate of shoot growth were measured under normal and constant cold temperature conditions (20–30°C in a greenhouse and 15°C in a growth chamber, respectively) as well as in an early planted field. Two early maturing lines, PI550666 and PI550597 (from Russia), appear to be better sources of germplasm than Shan Qui Red (from China) for germination and early seedling cold tolerance because of fewer undesirable characteristics. There were significant differences among genotypes under normal temperature conditions for both total germination percentage and rate of early shoot growth, whereas no significant differences were found in cold conditions. Of the two testers (female parents), N123A generally showed a negative combining ability for rate of germination in cold conditions, whereas crosses with tester N250A tended to be substantially better than the male parent. Selection for germination cold tolerance in seed parents will be more effective than in male parents. Though only inferred by this research, it is likely that differences in combining ability exist between seed parents for germination cold tolerance.