ABA-insensitivity of Alfalfa ( Medicago sativa L.) during seed
germination associate with plant drought tolerance
Abstract
Abscisic acid (ABA) is a vital stress resistant hormone of plant in
coping with adverse environmental conditions, such as drought stress.
Sensitivity of seed germination to exogenous ABA treatment could link to
different drought tolerance ability of different plant species. Here, we
selected alfalfa seedlings (S0-50) from seeds germinated under 50 μM ABA
treatment. The S0-50 plant showed more sensitivity in stomatal closure
to exogenous ABA and PEG treatments, and also stronger drought tolerance
than the plant of ABA-sensitive seed during germination (S0-0). Testing
of ABA content in leaf indicated that the S0-50 had a higher ABA content
in normal and under drought stress growth conditions than that of the
S0-0 plants. The seed of S0-50 next generation (S1-50) showed
significantly higher germination ratio under 50 μM ABA treatment, and
also had longer root after 15% PEG6000 treatment than the segregated
ABA-sensitive seed (S1-0). We found a cytosol-nucleus dual-localized PPR
protein gene MsSOAR1 was significantly highly expressed in S0-50
than in S0-0 plant. Overexpression of AtSOAR1, a negative
regulator in ABA-mediated Arabidopsis seed germination inhibition, and
also a homologous gene of MsSOAR1, significantly improved alfalfa
drought tolerance, branch number and plant height, and reduced the
expression level of ABA receptors MsPYL5 and MsPYL6. The
results suggest that ABA-insensitive during seed germination could
associate with repression of ABA signaling transduction. Selection of
alfalfa seedling during seed germination with exogenous ABA could be a
way to obtain drought tolerance germplasm, at least in ‘Zhongmu No.1’
alfalfa cultivar the plant material we used in the experiment.