The role of plant hormone abscisic acid (ABA) in plants under drought stress
(DS) is crucial in modulating physiological responses that eventually lead to adaptation to
an unfavorable environment; however, the role of this hormone in modulation of
glycinebetaine (GB) metabolism in maize particularly at the seedling stage is still poorly
understood. Some hydroponic experiments were conducted to investigate the modulation
role of ABA on plant growth, water relations and GB metabolism in the leaves of two
maize cultivars, Zhengdan 958 (ZD958; drought tolerant), and Jundan 20 (JD20; drought
sensitive), subjected to integrated root-zone drought stress (IR-DS) simulated by the
addition of polyethylene glycol (PEG, 12% w/v, MW 6000). The IR-DS substantially
resulted in increased betaine aldehyde dehydrogenase (BADH) activity and choline content
which act as the key enzyme and initial substrate, respectively, in GB biosynthesis.
Drought stress also induced accumulation of GB, whereas it caused reduction in leaf
relative water content (RWC) and dry matter (DM) in both cultivars. The contents of ABA
and GB increased in drought-stressed maize seedlings, but ABA accumulated prior to GB
accumulation under the drought treatment. These responses were more predominant in
ZD958 than those in JD20. Addition of exogenous ABA and fluridone (Flu) (ABAsynthesis inhibitor) applied separately increased and decreased BADH activity,
respectively. Abscisic acid application enhanced GB accumulation, leaf RWC and shoot
DM production in both cultivars. However, of both maize cultivars, the drought sensitive
maize cultivar (JD20) performed relatively better than the other maize cultivar ZD958
under both ABA and Flu application in view of all parameters appraised. It is, therefore,
concluded that increase in both BADH activity and choline content possibly resulted in
enhancement of GB accumulation under DS. The endogenous ABA was probably involved
in the regulation of GB metabolism by regulating BADH activity, and resulting in
modulation of water relations and plant growth under drought, especially in the drought
sensitive maize cultivar JD20.