A Review of Evidence on the Control of Shoot: Root Ratio, in Relation to Models

The influence of mineral nutrient availability, light intensity and CO2 on growth and shoot:root ratio in young plants is reviewed. Special emphasis in this evaluation is given to data from laboratory experiments with small Betula pendula plants, in which the concept of steady-state nutrition has been applied.

Growth and shoot: Root ratio of seedlings in relation to nutrient availability

This article reviews the current state of knowledge of the roles of iron in chloroplast structure and function and in chloroplast development. The uptake and transport of iron to leaves and the relationship of chlorophyll to leaf iron content are also reviewed briefly. In addition, we present some original data on the protein composition of thylakoid membranes and on chlorophyll biosynthesis as affected by iron deficiency and resupply.

Function of iron in chloroplasts

Arbuscular mycorrhizal fungi increased growth, nutrient uptake and tolerance to salinity in olive trees under nursery conditions.

Photosynthesis, assimilate partitioning and intracellular distribution of orthophosphate (Pi) in barly (Hordeum vulgare L.) leaves were measured in plants grown with either 25, 1 or 0 mmol· 1−1 nutrient phosphate supply. Phosphate deficiency resulted in a significant decrease in the leaf Pi, diminished rates of photosynthesis and a decrease in the sucrose/starch ratio in the leaves. Changes in the cytoplasmic Pi content were relatively small in comparison with the large variations in vacuolar Pi. The cytoplasmic Pi concentration was slightly higher in the leaves of plants grown at 25 mmol·l−1 Pi than in those grown at 1 mmol·l−1 Pi and was decreased in the phosphate-deficient plants in which photosynthesis was inhibited. With barley plants grown in phosphate-deficient media, very little, if any, Pi was present in the vacuole. All of the cellular Pi was in the cytoplasm. Barley, spinach (Spinacia oleracea L.) and soya (Glycine max L.) plants were grown to a comparative stage of phosphate deficiency as measured by leaf Pi levels. These species showed a uniform response to phosphate deficiency by increasing starch synthesis relative to sucrose but the accompanying limitation on photosynthetic capacity varied considerably among the species. Interspecific differences in assimilate partitioning between starch and sucrose were maintained over a wide range of Pi supply.

The relationship between phosphate status and photosynthesis in leaves : Effects on intracellular orthophosphate distribution, photosynthesis and assimilate partitioning.

Spinach plants were grown in nutrient-culture solutions containing reduced levels of all the macro- and micro-nutrient elements except cobalt and chlorine. The rates of photosynthesis (carbon dioxide fixation in the light expressed on a per unit chlorophyll or per unit fresh-weight basis) and respiration (carbon dioxide evolution in the dark expressed on a per unit nitrogen or per unit fresh-weight basis) for whole plants were measured using infra-red gas analysis techniques. Measurements were made when the plants displayed clear symptoms of deficiency relative to control plants. All nutrient deficiencies except iron and molybdenum depressed photosynthesis when chlorophyll was the basis of calculation; manganese-, copper-, phosphorus- and potassium-deficient plants showed the greatest depression. Alternatively when photosynthesis was calculated on a fresh weight basis calcium was the only deficiency which had no affect. Similarly when respiration was calculated on a nitrogen basis all deficiencies except iron, molybdenum and nitrogen result in depressed rates but when respiration was expressed on a fresh-weight basis potassium deficiency resulted in enhanced respiration rates and nitrogen, phosphorus, sulphur, manganese, zinc and molybdenum deficiencies resulted in reduced respiration rates.

J. V. Possingham

Papers

The effect of nutrient deficiencies on phosynthesis and respiration in spinach