Seed germination and dormancy traits of forbs and shrubs important for restoration of North American dryland ecosystems

In degraded dryland systems, native plant community re-establishment following disturbance is almost exclusively carried out using seeds, but these efforts commonly fail. Much of this failure can be attributed to the limited understanding of seed dormancy and germination traits. We undertook a systematic classification of seed dormancy of 26 species of annual and perennial forbs and shrubs that represent key, dominant genera used in restoration of the Great Basin ecosystem in the western United States. We examined germination across a wide thermal profile to depict species-specific characteristics and assessed the potential of gibberellic acid (GA₃ ) and karrikinolide (KAR₁ ) to expand the thermal germination envelope of fresh seeds. Of the tested species, 81% produce seeds that are dormant at maturity. The largest proportion (62%) exhibited physiological (PD), followed by physical (PY, 8%), combinational (PY + PD, 8%) and morphophysiological (MPD, 4%) dormancy classes. The effects of chemical stimulants were temperature- and species-mediated. In general, mean germination across the thermal profile was improved by GA₃ and KAR₁ for 11 and five species, respectively. We detected a strong germination response to temperature in freshly collected seeds of 20 species. Temperatures below 10 °C limited the germination of all except Agoseris heterophylla, suggesting that in their dormant state, the majority of these species are thermally restricted. Our findings demonstrate the utility of dormancy classification as a foundation for understanding the critical regenerative traits in these ecologically important species and highlight its importance in restoration planning.

Physio-biochemical assessment and expression analysis of genes associated with drought tolerance in sugarcane (Saccharum spp. hybrids) exposed to GA3 at grand growth stage

Drought is one of the most serious environmental factors limiting production of sugarcane worldwide. In order to assess the influence of gibberellins (GA₃ ) on drought and plant growth, along with associated physio-biochemical attributes, expression of eight drought-responsive genes were quantified and analysed. At grand growth stage (120 DAP) two sugarcane varieties (CoLk94184, CoPK05191) were exposed to drought by withholding irrigation. GA₃ (35 ppm) was applied using battery-operated uniform controlled dispensing sprayer twice at 1-week intervals on 2-week drought-stressed plants. Physio-biochemical attributes including antioxidant enzyme activities were estimated following standard protocols. RT-PCR was performed to visualise the drought-associated gene expression patterns. Drought triggered a reduction in RWC and chlorophyll content but these recovered when droughted plants were exposed to GA₃ . Proline content increased many fold in both varieties under stress, but decreased under the influence of GA₃ . There was a mixed response of antioxidant enzyme activity, which distinctly declined after GA₃ exposure, together with a lesser reduction in dry matter content over that of control plants. With increasing stress, expression of pyrroline-5-carboxylase synthetase (P5CS) and betaine-aldehyde dehydrogenase genes was observed, selectively up-regulated in CoPK05191. Expression of proline oxidase/transporter was high in CoPK05191 but diminished along with proline content after exposure to GA_3. CoLk94184 showed no significant difference in P5CS gene expression under stress condition, whereas expression of betaine-aldehyde dehydrogenase gene was unchanged in response to stress. Results demonstrated that exposure of droughted plants to GA₃ not only led to recovery of activity of drought-associated physio-biochemical attributes, but also minimised impact on cane dry weight and quality. Further, GA₃ application caused differential gene expression that possibly triggers increased responsiveness towards drought tolerance in sugarcane.