Plasticity in stomatal density and morphology in okra and tomatoes in response to soil and water salinity

Okra (Abelmoschus esculentus) and tomatoes (Lycopersicum esculentum) were grown in saline (3.0 dS m-1 NaCl) and non-saline soil and irrigated with saline (2.4 dS m-1 NaCl) or non-saline water to determine the response of stomatal density and morphology to salinity. Stomata density (stomata number per unit leaf area) for tomato grown on saline soil was reduced by 33% (12 mm-2) compared with those on non-saline soils (18 mm-2); this reduction was more severe on the adaxial leaf surface where stomatal density was low. Similar reductions in stomatal density were observed in tomato irrigated with saline water. Stomata size in tomato was significantly reduced by about 20% with both types of salinity, thus the proportion of leaf surface area occupied by the stomata in salt-stressed plants, i.e., stomata area index (SAI), averaged 4.4% in salt-stressed plants compared with 5.5% in plants grown in non-saline conditions. Okra, on the other hand, maintained a similar stomatal density (average 22 mm-2) on both saline and non-saline soils, but saline irrigation marginally increased the density. In okra, the abaxial leaf surface accounted for about 68% of the total stomata under both saline and non-saline conditions. Individual stoma size in okra was increased by up to 15% on both leaf surfaces due to salinity, hence, the SAI increased from an average of 9.0% under non-saline conditions to 11.7% under saline stress. Notwithstanding the increase in SAI for okra, salinity reduced stomatal conductance by more than 50% in both crops. The stomatal conductance was generally much larger in okra than in tomato, and was as large in okra exposed to salinity as for tomato in the absence of salinity

Biorefining of wheat straw:accounting for the distribution of mineral elements in pretreated biomass by an extended pretreatment–severity equation

BACKGROUND: Mineral elements present in lignocellulosic biomass feedstocks may accumulate in biorefinery process streams and cause technological problems, or alternatively can be reaped for value addition. A better understanding of the distribution of minerals in biomass in response to pretreatment factors is therefore important in relation to development of new biorefinery processes. The objective of the present study was to examine the levels of mineral elements in pretreated wheat straw in response to systematic variations in the hydrothermal pretreatment parameters (pH, temperature, and treatment time), and to assess whether it is possible to model mineral levels in the pretreated fiber fraction. RESULTS: Principal component analysis of the wheat straw biomass constituents, including mineral elements, showed that the recovered levels of wheat straw constituents after different hydrothermal pretreatments could be divided into two groups: 1) Phosphorus, magnesium, potassium, manganese, zinc, and calcium correlated with xylose and arabinose (that is, hemicellulose), and levels of these constituents present in the fiber fraction after pretreatment varied depending on the pretreatment-severity; and 2) Silicon, iron, copper, aluminum correlated with lignin and cellulose levels, but the levels of these constituents showed no severity-dependent trends. For the first group, an expanded pretreatment-severity equation, containing a specific factor for each constituent, accounting for variability due to pretreatment pH, was developed. Using this equation, the mineral levels could be predicted with R(2) > 0.75; for some with R(2) up to 0.96. CONCLUSION: Pretreatment conditions, especially pH, significantly influenced the levels of phosphorus, magnesium, potassium, manganese, zinc, and calcium in the resulting fiber fractions. A new expanded pretreatment-severity equation is proposed to model and predict mineral composition in pretreated wheat straw biomass