Turgor maintenance by osmoregulation in Brassica napus and B-juncea under field conditions

Indian mustard (Brassica juncea (L) Czernjacw) maintains higher leaf turgor than canola (B. napus L.) under water deficits and this is related to the greater yield of mustard under these conditions. The work reported in this paper was designed to study the way mustard maintains this turgor advantage. It was based on three field experiments that each used at least two cultivars or lines of each species. The leaf water potential at which leaves reached zero turgor was consistently lower in mustard than in canola (up to 1.1 MPa lower). This difference arose from a greater rate of decline in leaf osmotic potential with declining water potential in mustard rather than from any difference in the osmotic potential at full turgor. Calculations of solute accumulation showed that mustard had a greater capacity to osmoregulate than canola, with this capacity being the basis for its advantage in turgor maintenance. Other differences in plant water relations were consistent with the differences in osmoregulation, with the predicted relative water content of leaves at an osmotic potential of -2.5 MPa being 0.43 for canola and 0.61 for mustard. Mustard's greater capacity to accumulate solutes is concluded to be a major factor in its greater yield under water deficits. (C) 1997 Annals of Botany Company.