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