Natural rubber production and productivity have to be increased to meet the growing demands of rubber based industries

Transcription

1 IRC 212, KERALA, INDIA 2 Natural rubber production and productivity have to be increased to meet the growing demands of rubber based industries High yielding clones with increased tolerance to biotic and abiotic stresses is the only option under the changing climatic conditions Drought or water stress production of reactive oxygen species (ROS) and inhibition of antioxidant systems in plants Superoxide dismutase (SOD) activity first line of defence against ROS spontaneous dismutation of O 2 to H 2 O 2 SODs are classified into three groups Cu/ZnSOD mito, per, chl MnSOD mito, per FeSOD chl 1

2 GM Rubber 3 Genetically modified crops a major tool for addressing the harmful effects of environmental stresses. Different genes have been successfully transferred into several economically important crop plants worldwide increased protection against biotic and abiotic stresses Rubber Research Institute of India (RRII) recently developed genetically modified Hevea plants by over expressing MnSOD gene through Agrobacterium mediated genetic transformation in clone 4 2

3 5 MnSOD transgenic lines ( & ) and untransformed One year old bud grafted polybag plants Grown in protected area at Regional Research Station, Dapchari, Maharashtra One set of plants (n=6) of each line were irrigated daily; another set kept un irrigated for six days. Leaf sampling on the third day of drought treatment. After sixth day of drought treatment, the plants were irrigated daily to study the extent of drought recovery. 6 Solar radiation (photo radiometer, PMA 22) Gas exchange (Li 64 pps) Biomass partitioning (gravimetric measurements) Chlorophyll fluorescence (PAM 21 chlorophyll fluorometer ) Leaf water potential (Psypro water potential system) Total SOD activity Giannopolitis and Ries (1977). The leaf chlorophyll content (SPAD 52) Peroxidase activity Guilbault (1977). Relative water content Lipid peroxidation Heath and Packer (1968) 3

4 7 8 The weather conditions Solar radiation >2 μmol m 2 s 1 UV B radiation 4.2 Wm 2 Maximum temp C Minimum temp C Relative humidity 77% (morning) 5% (afternoon) Average sunshine hours 1 hrs. Irradiance (µmol m 2 s 1 ) Irradiance UV B UV B (Wm 2 ) Time (IST) 4

5 9 Transgenic lines showed more dry matter partitioning towards the taproot. 7 Root:shoot ratio was.75 for untransformed line, 1.2 for and 1.5 for. Increased biomass accumulation in the root under dry environments defensive mechanism to overcome drought stress. Since the rootstocks are different it needs to be studied whether the increased biomass allocation to root is a consequence of genetic modification. Dry matter (g) Lateral root Tap root Stem Leaf blade Petiole 1 Under moisture stress, tissue water potential and water content are maintained close to the unstressed level by increasing the water uptake or limiting the water loss maintained better Ψ L throughout. Decline in Ψ L was more in the untransformed plants. Recovery of ψ L was similar in all the lines RWC declined from 84 87% to 62 68% indicating moderate to severe stress The tissue water content was higher in 6 transgenic lines than untransformed 55 5 ψ L (MPa) RWC (%)

6 11 7 No significant variation in chlorophyll content index among the lines studied Chlorophyll content index (SPAD) Little variation in ΦPSII under moisture stress Phi PS R1 R2 R3 had much lower PSII activity after 3 rd day of drought treatment. All the clones recorded the lowest ΦPSII value on the 7 th day. The plants showed symptoms of drying after six days of moisture stress, while it takes two weeks in traditional region The rapid development of drought reason for low response obtained in chlorophyll content and chlorophyll fluorescence parameters, which usually take longer time for responding to stress conditions, unlike gas exchange parameters. 6

7 13 Progressive decline in CO 2 assimilation with water stress. CO 2 assimilation reached near zero after three days of moisture stress in and ; fifth day in Recovery was better in the transgenic lines Decreased CO 2 diffusion from the atmosphere to the site of carboxylation under water limitation decreased photosynthesis role of stomata? PN (µmol m 2 s 1 ) R1 R2 R3 14 Stomatal closure is an immediate response of the plant to soil moisture stress. It reduces the availability of CO 2 for photosynthesis, leading to the formation of ROS due to excess electrons. Sharp decline in g s noticed in. g s (mol m 2 s 1 ) Transgenic lines showed better recovery of g s compared to untransformed g s reduced by 42% in, 3% in and more than 62% in untransformed after 24 hours R1 R2 R3 7

8 15 SOD activity was higher in, and untransformed showed comparable activity under drought. Peroxidase activity was low in all lines Drought treatment did not induce any major change in the peroxidase activity SOD (units) Peroxidase (units) Control Drought Control Drought 3.12± ±.24.84±.5.89± ± ±.71.52±.4.28± ± ±.5.33±.3.77±.5 The antioxidant enzymes activity did not show a consistent response 16 MDA (µmol g 1 fw 1 ) Control Drought 2.12±.4 3.2± ± ± ± ±.2 Lipid peroxidation was higher in compared to other lines Varied activity of antioxidant ezymes under water deficit in Hevea, though the relative transcript abundance was stable and reproducible (Leclercq et al., 212). Transgenic tobacco over expressing MnSOD enhanced tolerance to oxidative stress only in the presence of other antioxidant enzymes and substrates genotype and isozyme composition (Slooten et al., 1995). Faulty function of the antioxidant gene products, physiological targets studied, the severity of the stresses imposed, and/or the plant systems used attributed for the low response of transgenic plants 8

9 17 Transgenic lines performed better under dry conditions in terms of water relations and photosynthetic parameters Among the transgenic lines, line was better Antioxidant enzymes did not show a consistent response under drought in all the clones The mechanisms involved in tolerance to drought stress in transgenic lines need further investigation 9