Turgor Maintenance by Osmoregulation inBrassica napusandB. junceaunder Field Conditions

Indian mustard (Brassica juncea(L) Czernjacw) maintains higherleaf turgor than canola (B. napusL.) under water deficits andthis is related to the greater yield of mustard under theseconditions. The work reported in this paper was designed tostudy the way mustard maintains this turgor advantage. It wasbased on three field experiments that each used at least twocultivars or lines of each species. The leaf water potentialat which leaves reached zero turgor was consistently lower inmustard than in canola (up to 1.1 MPa lower). This differencearose from a greater rate of decline in leaf osmotic potentialwith declining water potential in mustard rather than from anydifference in the osmotic potential at full turgor. Calculationsof solute accumulation showed that mustard had a greater capacityto osmoregulate than canola, with this capacity being the basisfor its advantage in turgor maintenance. Other differences inplant water relations were consistent with the differences inosmoregulation, with the predicted relative water content ofleaves at an osmotic potential of -2.5 MPa being 0.43 for canolaand 0.61 for mustard. Mustard's greater capacity to accumulatesolutes is concluded to be a major factor in its greater yieldunder water deficits. Brassica napusL.; Brassica juncea(L) Czernjacw; Indian mustard; canola; water deficit; plant water relations; osmoregulation; osmotic adjustment; turgor