ABSTRACT
The present study evaluated three wheat genotypes (SD-28, SD-32 and
Chirya-1) were evaluated for physiological attributes like Relative
Water Content, Proline Content, Membrane Stability Index and Chlorophyll
Content where Opata was used as a control check under three different
levels of drought stress (100% FC, 80% FC and 60% FC). Results
revealed that chlorophyll content was significantly affected under
stressed conditions in all the studied genotypes and genotypes.
Molecular diagnosis of the selected wheat genotypes and genotypes was
carried out with RT-PCR using expression profile of 06 genes
(TaLhca1, TaLhca2, TaLhca3, TaLhcb1, TaLhcb4 and TaLhcb6 )
that encodes for LHCI and LHCII proteins. RT–PCR indicated variable
expression of the selected genes in response to different level of
drought stress. The results obtained clearly showed the relation between
genotypes and severity of drought stress condition. Among the studied
genotypes Chirya-1 and SD-28 performed well with higher level of gene
expression under drought stress condition; and may be considered drought
tolerant genotypes with potential to enrich the genetic background of
locally adapted wheat lines against drought stress.
Key Words: Wheat; Drought Stress; Stay-Green; Gene Expression;
Physiological attributes.
INTRODUCTION
Importance of wheat as staple food is well known as being life line of
35% of the world population. But in past two-three decades,
unpredictable climatic conditions have resulted in stagnation in wheat
production. Drought is a major environmental stress, which can effect
growth of cereals crops and has decreased the production and performance
of the plant (Shao et al. , 2009), (Rad et al. , 2012). The
significant rise in drought stress condition has enforced us to develop
climate resilient high yielding genotypes; hence, there is a need to
develop better understanding of the traits which respond to drought by
exploiting key traits (Halford and Hey, 2009) It has been suggested that
due to climatic changes, the shortage of water may be increased which
will affect the cereals crops in many areas of the world.
Leaf senescence is an intricate process where various cellular processes
occurs consistently, parallel or sequentially (Lim et al. , 2007).
It normally starts with change in genes expression and genes are
expressed by environmental stimuli during various developmental stages.
If senescence starts at mature stage then the changes will not appear at
earlier stages of senescence until the stress is applied at initial
stages. These changes include the chlorophyll pigment breakdown normally
followed by break down of mitochondria, plastids, nuclei and vacuoles,
which leading to death of cell (Buchanan-Wollaston and Ainsworth, 1997).
To know about the whole mechanisms of leaf senescence it is important to
dissect the leaf senescence process one such approach is to evaluate
transgenic plants which show different leaf senescence phenotype which
we called stay green (Kusaba et al. , 2013).
Two main types of chlorophyll are present in higher plants, Chlorophylla and Chlorophyll b . Chlorophyll a is a part of all
chlorophyll–protein complexes, whereas Chlorophyll b is confined
only in PSI-associated light-harvesting complex I (LHCI) and
PSII-associated LHCII. Light-harvesting complex I and light-harvesting
complex II are present in thylakoid membranes and its function is energy
production and transfer. LHCII is mostly present in grana, and due to
intermolecular forces its main function is formation and maintenance of
grana stacks (Allen and Forsberg, 2001). The Lhca and Lhcbgene families encoded the apoproteins of light-harvesting complex I and
light-harvesting complex II respectively. Lhca1–Lhca4 genes
formed the protein of LHCI which are associated with PSI. Lhcb1 ,Lhcb2 , and Lhcb3 genes code the polypeptides of trimeric
LHCII. Lhcb4, Lhcb5, and Lhcb6 proteins (also known as CP29, CP26, and
CP24,) are proposed to be monomeric proteins which are found one set per
PSII unit. The Lhca and Lhcb genes expression and LHCI and LHCII
stability are very important to keep the photosynthetic process at high
level (Standfuss et al. , 2005).
One of the most important goals of researcher to increase grain yield
and it can be achieved by improving the rate of photosynthesis or by
carbon assimilation (Zhu et al. , 2010) the approach to achieve
this goal would be to delay senescence alongside the photosynthetic
activity of plant for lengthier period of time (Dohleman and Long,
2009). To achieve these objectives in wheat plant, it is necessary to
understand the leaf senescence mechanisms at molecular level.
In the present study, the selection and photosynthetic characteristics
of ‘stay green’ mutants of wheat are described and to characterize wheat
genotypes in their response to drought stress. The characterization was
focused on both physiological and molecular aspects of wheat genotypes
to select the wheat genotype with desirable traits