Role of abscisic acid in legumes under abiotic stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 148

Xylem

Nuclear zeaxanthin

antheraxanthin

ER all- trans -violaxanthin

OPA

cytosol

9 ʹ - cis -violaxanthin
all- trans -neoxanthin

PA

Xanthoxin

8 ʹ -hydroxy ABA

abscisic aldehyde

9 ʹ - cis -neoxanthin

ABA-GE A B A

ABA Xanthoxin

OH

O O OH

Plastid

ABA

Vacuole

ABA-GE (inactive)

ABA ABA

OH

O O OH

ABA-GE ABA

ABA (bioactive)

Apoplast

ABA-GE ABA-GE

Figure 10.1 Abscisic acid ( ABA) biosynthesis and catabolism pathways. The steps from zeaxanthin to xanthoxin in de novo ABA
synthesis occurring in plastids are shown. Xanthoxin moves from the plastids to the cytoplasm and is converted to ABA. In the
catabolic pathways, ABA is inactivated through either oxidation or conjugation. Hydroxylation as well as hydrolysis of ABA-GE is
shown with the corresponding enzymes. Postulated pathways are shown by broken lines and the confirmed pathways are shown
as solid lines. ER, endoplasmic reticulum; PA, phaseic acid; DPA, dihydrophaseic acid; ABA-GE, ABA glucosyl ester. Adapted from
Xu et al. (2013).

investigations have studied the ABA-GE role in legumes,
and the molecular mechanism underlying the transport
of ABA or its conjugates remains unclear.
Recently, some investigations have intensively studied
the specific enzymes of the ABA 8′-hydroxylation reac-
tion in plants. These enzymes are members of the
cytochrome P450 (CYP) superfamily, named CYP707A.
Kushito et al. (2004) isolated four genes of the CYP707A
superfamily that encode ABA 8′-hydroxylase in
Arabidopsis . Further, Vallabhaneni and Wurtzel (2010)
identified three genes of this superfamily from bean.
These investigations established that the genes of
CYP707A superfamily are mainly regulated at the tran-
scriptional level and control ABA levels under adverse

conditions. Zheng et al. (2012) identified and analysed
the function of the CYP707A gene family isolated from
soybean under dehydration and salt stresses. The
construction of a cyp707a2T-DNA knock-down mutant
showed overexpressed soybean GmCYP707A1 and was
a single mutant that reported a significant phenotype
related to seed germination under ABA treatment
(Kushiro et al., 2004). A series of experiments analysing
the germination rate indicated that GmCYP707A1a pos-
sibly encodes an ABA 8′-hydroxylase due to the
complementation of overexpression of GmCYP707A1a
to AtCYP707A2. Alteration of ABA sensitivity by the
loss of function of AtCYP707A2 was reflected by pri-
mary root growth, formation of lateral roots and