Effect of Salt Stress on Callus Cultures of Oryza sativa L.

Kavi Kishor, P.B 1988. Effect of salt stress on callus culturesof Oryza sativa L.—. exp. Bot 39 235–240 Callus cultures of rice adapted to grow under increasing NaClstress were found to accumulate considerable amounts of freeproline, compared with unadapted cells. Salt-adapted cells grownfor 10 passages (25 d each) on NaCl-free medium accumulatedproline on re-exposure to salt as did cells which were growncontinuously on NaCl. On replacing NaCl (100 mol m^–3)with 100 mol m^–3 of KC1, fresh and dry weights as wellas free proline content of salt-adapted callus declined comparedto that attained on 100 mol m^–3 NaCl medium. However,equimolar concentrations of NaCl and KC1 (when added together)produced an increase in growth and free proline accumulationin salt adapted callus. Omission of Ca²⁺ from the growth mediuminhibited the growth of salt-adapted cells in the presence ofNaCl, while it had little effect on the growth of non-adaptedcells in the presence of NaCl. ABA increased the fresh and dryweights of the non-adapted callus only in the presence of 200mol m^–3 of NaCl but not in the absence of NaCl. ABA failedto evoke the same response in salt adapted cells in the presenceof the salt. Tissues exhibited good growth under inhibitorylevels of NaCl (500 mol m^–3) only when glycine betaine,choline and proline were added to the medium but showed no growthin the presence of sarcosine, glycine and dimethylglycine. Key words: Oryza saliva, callus cultures, NaCl stress     

Salt stress in cultured rice cells: effects of proline and abscisic acid

Abstract. The presence of 1 and 10 mol m⁻³ proline in media containing 100 and 200 mol m⁻³ of NaCl, had little effect on the growth of salt-adapted callus of rice. However, in such callus proline accumulation was stimulated by 10 mol m⁻³ proline in the presence of 100 mol m⁻³ NaCl. On the other hand, with 100 mol m⁻³ NaCl, both 1 and 10 mol m⁻³ proline significantly increased both the growth and proline content of salt-unadapted callus. On replacing NaCl with KCl (100 and 200 mol m⁻³), growth of saltadapted as well as unadapted callus was inhibited, but the presence of 10 mol m⁻³ proline had an ameliorating effect. Abscisic acid (ABA) supressed the growth of both salt-adapted and unadapted callus of rice in the absence of salt stress. ABA inhibited the growth of callus adapted to and grown in 100 and 200 mol m⁻³ of NaCl or when it was replaced by equimolar concentrations of KCl. Growth of 100 mol m⁻³ NaCl adapted cells was inhibited when they were transferred to a medium containing 200 mol m⁻³ of NaCl, but in the presence of ABA it was stimulated. ABA increased the growth of unadapted cells when subjected to different salts. Also, ABA accelerated the adaptation of cells exposed to salt but not to water deficits imposed by nonionic solutes.     

Is proline accumulation per se correlated with stress tolerance or is proline homeostasis a more critical issue?

Proline has been recognized as a multi‐functional molecule, accumulating in high concentrations in response to a variety of abiotic stresses. It is able to protect cells from damage by acting as both an osmotic agent and a radical scavenger. Proline accumulated during a stress episode is degraded to provide a supply of energy to drive growth once the stress is relieved. Proline homeostasis is important for actively dividing cells as it helps to maintain sustainable growth under long‐term stress. It also underpins the importance of the expansion of the proline sink during the transition from vegetative to reproductive growth and the initiation of seed development. Its role in the reproductive tissue is to stabilize seed set and productivity. Thus, to cope with abiotic stress, it is important to develop strategies to increase the proline sink in the reproductive tissue. We give a holistic account of proline homeostasis, taking into account the regulation of proline synthesis, its catabolism, and intra‐ and intercellular transport, all of which are vital components of growth and development in plants challenged by stress.     

Activity of Wall-bound Enzymes in Callus Cultures of Gossypium hirsutum L. During Growth

Activities of - and ß-glucosidase, - and ß-galactosidase,-mannosidase, ß-1,3-glucanase, acid and neutral invertaseswere detected in the cytoplasmic fraction as well as in cellwalls isolated from callus cultures of cotton. Activity of ß-mannosidase,however, could not be detected in the cell walls. Transfer ofcallus to a fresh medium did not immediately influence the activitiesof -glucosidase and ß-galactosidase but increasedsignificantly ß-glucosidase, -mannosidase, acid andneutral invertases. Addition of cycloheximide (1 and 100 mgl^–1) further stimulated acid and neutral invertases butnot other enzymes tested. Sodium chloride (NaCl) was effectivein extracting a-glucosidase, ß-glucosidase, ß-galactosidase,acid and neutral invertases. EDTA extracted most of the -galactosidase,-mannosidase, ß-1,3-glucanase and some -glucosidase.But, NaCl and EDTA could not extract some of the - and ß-glucosidasesand also acid and neutral invertases as evidenced from the residualand extra cellular activity. Studies with whole cells as a sourceof enzyme revealed that some of these enzymes were associatedwith the cell surface. Callus, glycosidases, glucanase, growth, Gossypium hirsutum