Sana Fatima

Structural Features of Some Wheat (Triticum Spp.) Landraces/Cultivars Under Drought and Salt Stress

Seven local landraces of common and durum wheat (Triticum aestivum L. and T. durum L.) from the arid and semi-arid areas of the Sultanate of Oman were examined for specific leaf and stem structural features for water conservation. On the basis of shoot fresh and dry weights (g plant−1), degree of tolerance to drought and salt stresses in these wheat landraces/cultivars can be ranked as S-24 > J-305 > Sarraya > Senain > Cooley > MH-97 > Missani>Hamira > Shwairaa. Modifications related to water conservation were found to be high degree of sclerification, succulence in leaf and stem, low resistance to water conductance in vascular tissue, and pubescence on leaf surface. The salt and drought tolerant cultivar S-24 showed high proportion of chlorenchyma and intensive sclerification in stem structure, and well-developed bulliform cells and dense pubescence on the leaves. These modified features were poorly developed in lesser stress tolerant Omani wheat landraces like Hamira and Shwairaa. Accession Senain also showed stem succulence (solid stem), an important xeromorphic feature. Structural modifications in landrace Missani were found to be increased sclerification in vascular tissue and high number of metaxylem vessels and high proportion of parenchyma in stem, and highly developed bulliform cells in leaf. Overall, the promising anatomical traits in highly stress tolerant landraces/cultivars were chlorenchyma in stem, rigorous sclerification in parenchyma and around vascular tissue, stem and leaf succulence, and enhanced ratio of major conducting tissue.

Physiological adaptative characteristics of Imperata cylindrica for salinity tolerance

Two populations of cogongrass [Imperata cylindrica (L.) Raeuschel], one from the saline regions of the Salt Range and the other from the non-saline regions of Faisalabad were assessed for salinity tolerance on the basis of some key morphological and physiological attributes. It was hypothesized that the tolerant population from the Salt Range must have developed some specific structural modifications, which are responsible for its better survival under high salinities. These adaptive components can be effectively used in modern technologies for improving degree of tolerance of other sensitive crops. The population from the Salt Range markedly excelled the Faisalabad population in terms of growth and physiological attributes measured in this study. The Faisalabad population of I. cylindrica was unable to survive at the highest salt level (200 mM NaCl). The tolerance of the Salt Range population to salt stress was found to be related to high accumulation of organic osmotica, particularly total free amino acids and proline as well as Ca2+ in the shoot. The distinctive structural modifications in the Salt Range population were found to be enhanced succulence, well-developed bulliform cells in leaves and smaller stomatal area.

Ecotypic adaptations in Bermuda grass (Cynodon dactylon) for altitudinal stress tolerance

Abstract Three ecotypes [foot hill (700 m), mid hill (1571 m) and top hill (2804 m)] of a Bermuda grass Cynodon dactylon (L.) Pers. from Pir Chinasi Hill in Western Himalaya were evaluated for their degree of tolerance to altitudinal stress. Differential response of all ecotypes in terms of adequate structural modifications to different elevation levels was an evident to confirm the hypothesis that plants inhabiting different altitudes show variation in structure (internal modifications) and strategic (response) due to heterogeneity in environmental gradients. Soil at top hill site was more acidic and displayed significant increase in ionic content and total nitrogen. High elevation had severe impact on morphoanatomical and physiological attributes. A significant decline in shoot fresh weight and total leaf area was observed in top hill ecotype. With exception of Ca2+ and carotenoid, other ionic and chlorophyll content were significantly declined at high elevations. Anatomical alterations such as, increased leaf thickness, intensive sclerification around the vascular bundle and pith area, reduced metaxylem vessel area, high number of silica bodies, high pubescence (increased microhair and trichome density) were some of the promising anatomical adaptations in top hill ecotype which played an important role in high degree of tolerance of this grass to cope with altitudinal stresses. Increased leaf thickness might be a response to lower temperature that protects mesophyll cells and high density of trichomes may be involved in blocking transpiration water and internal heat. The pattern of constant variation suggests that differential response of these ecotypes is highly related to air temperature, pattern of rainfall, availability of nutrients.

Physio-Anatomical Responses of Plants to Heavy Metals

Environmental pollution caused by heavy metals is a global issue, which seriously affects growth and development of agricultural crops, as well as the native flora. It is known that metal toxicity can significantly alter soil physico-chemical properties of the soil, mainly organic matter, pH and cation exchange capacity. The devastating impact of heavy metals may be related to retarded growth and development, ionic imbalance, metal toxicity, reduced photosynthetic rate, degradation of chloroplast and photosynthetic pigments, and more importantly disturbed plant water relation. Heavy metal in the soil can also induce alterations in anatomical parameters. Among anatomical changes, disintegration and reduced size of parenchymatous tissue, reduced size of xylem vessels, degraded and smaller mesophyll tissue, and as a whole reduced root and stem diameter and leaf growth. Moreover, there is a spatial accumulation of heavy metals in different organs, more commonly in dermal, parenchymatous and phloem tissues. However, tolerance to heavy metals varies among different species, and even within populations of a same species. Overall this chapter describes how far heavy metal toxicity can promote the development of specific structural and functional modifications in plants exposed to metal-enriched environment and how these features could help plants to thrive well under such harsh conditions.

Adaptive components of tolerance to salinity in a saline desert grass Lasiurus scindicus Henrard

Five differently adapted natural populations of the native salt desert grass Lasiurus scindicus Henrard from Lesser Cholistan Desert (Pakistan) in South Punjab of east central Pakistan, were evaluated to examine their mechanism of adaptation to saline stress based on some key morpho–anatomical and physiological characteristics. Five ecotypes were collected from one saline site, two moderately saline sites, and two highly saline sites. Anatomical adaptations in each ecotype critically supported the physiological, but the adaptations were of specific nature depending on the type of each site’s normal habitat conditions. Higher salinities resulted in increased Na+, Cl−, Mg2+, Ca2+ and K+ content in root and shoot. At root level, some specific structural modifications like increased sclerification in cortical and pith regions, endodermal thickness, and number and size of xylem vessels are vital for water conservation under osmotic stress. Several characteristics were promising for increasing the plants ability to deal with osmotic stress, including at the stem level, increased sclerification, stem area, cortical region thickness and vascular bundle area, and at the leaf level, significant structural modifications such as leaf thickness, epidermal thickness, sclerenchymatous area, cortical area, metaxylem area and bulliform cell area were promising. All these may contribute towards water conservation, which ultimately account for ecotype survival under saline–induced physiological droughts.