Physiological Changes in Cultured Sorghum Cells in Response to Induced Water Stress

Abstract

ABSTRACITen varieties of Sorghum bicolor (L.) Moench were grown as callus cultures under conditions of water stress, which was induced by addition of polyethylene glycol (molecular weight 8000) in the medium. Growth and free proline were estimated in the control and water-stressed cultures. In all varieties, proline levels were low in the absence of water stress and the levels increased in response to water stress. However, the magnitude of these increases were not correlated with stress tolerance of the individual varieties in culture. Thus increase in proline seems to be an incidental consequence of stress in vitro and not an adaptive response to combat water stress in sorghum.Drought stress is very common in the sorghum-growing regions of the world, and several distinct varieties have evolved with varying degrees ofdrought tolerance (1). There are different mechanisms by which plants cope with water stress. One of the physiological responses to drought is the accumulation of intracellular solutes (16,18). These are generally low mol wt metabolic products such as carbohydrates, amino acids, sugar phosphates, etc. The extent to which each of these plays a role in osmotic adjustment varies with the species. Accumulation of solutes in response to water deficits has been observed in leaves ofsorghum (2,8,9). A similar phenomenon was also observed when plant cells were cultured under conditions of induced water stress using PEG (5). It was further shown that PEG itself did not contribute significantly to the osmotic adjustment (4).There is virtually no information about the physiology of sorghum callus grown in vitro under osmotic stress. Recently, we have been able to show a certain degree of correlation between drought responses in the field and response to water stress in culture (manuscript in preparation). In this study, an attempt was made to analyze free proline levels in sorghum when grown as callus cultures with and without addition ofPEG in the culture medium. The rationale was that this approach would enable us to look for any inherent differences at the cellular level that make some varieties better than others in terms of drought tolerance. advantage to any variety to cope with water stress. Such knowledge is fundamental in selecting genotypes for breeding for drought tolerance. MATERIALS AND METHODSCallus Cultures. Callus cultures were initiated from sorghum seeds using the procedure of Smith et al. (14). Seeds of Sorghum bicolor(L.) Moench varieties B35, RTx7078, RTx7000, RTx432, BTx3197, BTx623, 1790E, RTx430, R9188, and BTx378 were used in our experiments. Callus was subcultured at 4-week intervals until enough callus material was obtained to start them on the stress media. All calli were less than 6 months old when they were subjected to osmotic stress.Water Stress. PEG, mol wt 8000, was added to the growth medium at concentrations of 5, 10, 15, 20, and 25% (w/v) before adjusting the pH of the medium to 5.7. Twenty-five ml of medium was distributed into each culture tube and Heller supports ...

Proline Accumulation and Its Implication in Cold Tolerance of Regenerable Maize Callus

“…DISCUSSION Regenerable callus from maize inbred lines B37wx, H99, and Pa9 1 can be induced to tolerate 4C for twice as long as untreated control callus (at least 100 d), with treatments that increase the free proline concentration in the callus (Table I). This observation is similar to other reports in the literature that have linked proline accumulation, in both callus and whole plants, to cold and drought stress tolerance (1,5,8,9,(17)(18)(19)(20)(21)(22). The exact role of proline in the cold tolerance of maize callus is unknown.…”

“…Similarly, cultured plant cells have been shown to accumulate proline when placed under salt or osmotic stress (1,8,17,21) and proline has been used to protect a nonregenerable suspension of the maize inbred B73 from exposure to liquid N2 (22).…”

In vitro selection and characterization of polyethylene glycol (PEG) tolerant callus lines and regeneration of plantlets from the selected callus lines in sugarcane (Saccharum officinarum L.)

“…Addition of PEG to the medium produces osmotic stress (Kumar et al 2011) and decreases the water potential (Aazami et al 2010) which negatively effects growth. Decreased growth in the presence of PEG in the medium is reported in sugarcane (Errabii et al 2008) sunflower (Hassan et al 2004) Sorghum (Bhaskaran et al 1985) tomato (Abdel-Raheem et al 2007;Aazami et al 2010). …”

“…A similar trend in proline levels is reported in tobacco (Gangaopadhyay 1997) sunflower (Hassan et al 2004). Increase in the proline accumulation on exposing calli to PEG is reported in Sorghum (Bhaskaran et al 1985) rice (Aqeel-Ahmad et al 2007) Proline accumulation under water deficit has been mainly recognized as an osmotic agent (Handa et al 1986). Selected calli exhibited osmotic adjustment in response to PEG stress through the synthesis of solutes like proline.…”

Characterization of a rice gene showing organ-specific expression in response to salt stress and drought.

“…This defense is augmented by increases in the concentrations of various osmoprotectants including proline, sugars, and organic acids (Handa et al, 1983;Steward and Voetberg, 1985;Binzel et al, 1987). Several studies, however, have indicated that proline levels do not necessarily correspond to the tolerance of plants for salt and may be induced only after damage has been sustained (Bhaskaran, Smith, and Newton, 1985;Chandler and Thorpe, 1987;Moftah and Michel, 1987). It may be that some of the heat shock proteins produced by salt stress (Heikkila et al, 1984;Harrington and Aim, 1988) similarly are needed to cope with damaged cellular components.…”