Elucidation of molecular mechanisms governing cold tolerance during reproductive stage in chickpea Cicer arietinum L

Abstract

Low temperature induced flower abortion in chickpea (Cicer arietinum L.), an important food grain legume in India, is the major cause of reduced yields in winter sown chickpea in India. However, exact causes of flower abscission by cold stress (CS) in chickpea, especially the impact of CS on male gamete development are largely unknown. Similarly, flower development and anther/pollen development in chickpea are also not known. In the present study, flower development stages (12 stages; stages 7-18) and anther/pollen development stages (11 stages; stage 4-14c) were identified in chickpea. A user friendly criterion based on flower length and flower stage to estimate anther stage was also described. In addition to this, the causes of aberrations in male gamete formation in cold-susceptible genotype GPF2 were also investigated under CS (4°C and 9°C). The abortion of flowers at early flower stages was due to disruption of microsporogenesis, microgametogenesis, tapetum degeneration and anther dehiscence, whereas abortion of older flowers was due to reduction in pollen viability, ovule viability, stigma receptivity and pollen load on stigma. Male and female reproductive organ development as well as flower development under CS in GPF2 was compared with (cold-tolerant) ICC 16349 genotype. The studies revealed that 4°C temperature was too low for expression of cold-tolerance in chickpea and evaluation of cold-tolerance in chickpea should be carried out at 9°C. At 9°C, the growth of plants, flowers, anthers and gynoecium was better in ICC 16349 than that in GPF2. The molecular mechanisms of anther development in cold-tolerant ICC 16349 under CS were also investigated. ICC 16349 anthers under CS maintained normal carbohydrate pool (reducing sugars, non reducing sugars and starch), whereas GPF2 anthers failed to do so. Apart from carbohydrates, the antioxidant enzymes glutathione reductase and ascorbate peroxidase also appeared to contribute to cold tolerance in ICC 16349 anthers. Higher levels of proline in ICC 16349 anthers under CS were due to increased transport of proline to anthers as evident from higher expression of transporter of proline called PT 1. Further studies using whole genome transcriptomics are expected to elucidate other genes involved in cold tolerance by chickpea anthers. newline