Growth and Photosynthetic Responses to Manganese and Copper Deficiencies in Wheat (Triticum aestivum) and Barley Grass (Hordeum glaucum and H. leporinum)

Abstract

Wheat and barley grass were raised as seedlings in aerated solution cultures under high-pressure sodium vapour lamps in a growth cabinet. Manganese and copper were provided over a wide span of concentrations to induce a range in deficiency symptom expression. Plant response was documented in terms of biomass gain, in vivo chlorophyll fluorescence, CO₂-saturated O₂ evolution by leaf slices, single leaf H₂O/CO₂ exchange and A(p_I) curves (assimilation as a function of intercellular CO₂ partial pressure) at saturating light.

Photosynthetic dysfunction due to trace element deficiency lowered O₂ evolution (both area and chlorophyll basis) and slowed down leaf gas exchange. Both initial slope and CO₂-saturated phases of A(pi) curves were similarly affected in the two species under either Cu or Mn deficiency.

Induction kinetics of in vivo chlorophyll fluorescence proved distinctive for both species. Mn deficiency was often manifest as increased constant-yield (F_o) in combination with much reduced variable fluorescence (F_v). Increased ratio of F_o/ F_v was confirmed as a useful index for early diagnosis of Mn deficiency regardless of leaf Cu status.

Barley grass (both H. glaucum Steud. and H. leporinum Link) was more tolerant of low Mn and Cu status than wheat, especially in terms of growth and photosynthetic response to Mn deficiency. Wheat plants made little growth once Mn supply was reduced to 10% of control level whereas barley grass was only moderately constrained.