Heterosis for water uptake by maize (Zea mays L.) roots under water deficit: responses at cellular, single-root and whole-root system levels

To examine the potential heterosis for water uptake by maize roots, the hydraulic properties of roots in the F1 hybrid （Hudan 4） were compared with those of its inbred parents （ 478 and Tian 4） at cellular, single-root and whole-root system levels under well-watered and water-deficit conditions. The cell hydraulic conductivity （Lpc） decreased under water deficit, but the Lpc of the F1 was higher than that of its inbred parents with or without stress from water deficit. Marked reductions in Lpc were observed following Hg2＋ treatment. The hydrostatic hydraulic conductivity of single roots （hydrostatic Lpsr） varied among genotypes under the two water treatments, with the highest in the F1 and the lowest in 478. Radial hydraulic conductivity （radial Lpsr） and axial hydraulic conductance （Lax） of the three genotypes varied similarly as Lpsr. The variations in hydraulic parameters were related to root anatomy. Radial Lpsr was negatively correlated with the ratio of cortex width to root diameter （R2=-0.77, P〈0.01）, whereas Lax was positively correlated with the diameter of the central xylem vessel （R2=0.75, P〈0.01） and the cross-sectional area of xylem vessels （R2=0.93, P〈0.01 ）. Hydraulic conductivity （Lpwr） and conductance （Lwr） of the whole-root system followed the same trend under the two water treatments, with the highest values in the F1. The results demonstrated that heterosis for water uptake by roots of the F1 occurred at cellular, single-root and whole-root system levels under well-watered and water-deficit conditions.

Two New Group 3 LEA Genes of Wheat and Their Functional Analysis in Yeast

The group 3 late embryogenesis abundant （LEA） proteins are thought to protect cells from stresses associated with dehydration during periods of water deficit. To investigate the functions of different members of the group 3 LEA genes, we isolated and characterized two new group 3 LEA genes, namely TaLEA2 and TaLEA3, from wheat （Triticum aestivum L.） and introduced TaLEA2 and TaLEA3 into Saccharmyces cerevisiae to examine the effect of these genes on yeast cell tolerance to osmotic, salt, and cold stresses. The TaLEA2 gene encoded a protein of 211 amino acids and possessed five repeats of 11-mer amino acid motifs. The TaLEA3 gene encoded a polypeptide of 211 amino acids with nine repeated units. Overexpression of TaLEA2 and TaLEA3 improved stress tolerance in transgenic yeast cells when cultured in medium containing sorbitol, salt and-20℃ freezing treatments respectively. However, the yeast transformants with TaLEA2 seemed to be more tolerant to hyperosmotic and freezing stress than transformants with TaLEA3. This implies that a close relationship exists between function and the number of repeats of the 11- mer amino acid motif in the group 3 LEA protein.

Advances in Biological Water-saving Research:Challenge and Perspectives

Increasing the efficiency of water use by crops continues to escalate as a topic of concem because drought is a restrictive environmental factor for crop productivity woridwide .Greater yield per unit rainfall is one of the most important challenges in water-saving agriculture Besides water-saving by irrigation engineering and conservation tillage, a good understanding of factors limiting and/or regulating yleld now provides us with an opportunity to identify and then precisely seiect for physiciogical and breeding traits that increase the efficiency of water use and drought tolerance under water-limited conditions, biological water-saving is one means of achieving this goal, A definition of bilogical water-saving measures is proposed which embraces improvements in water use efficiency （WUE） and drought tolerance, by genetic improvement and physiological regulation. The preponderance of bilogical water-saving measures is discussed and strategies identified for working within natural resource constraints. The technology and future perspectives of bilogical water saving could provide not only new water-saving techniques but also a scientific base for application of water-saving irrigation and conservation tillage.

Fighting for the poverty:a case study for human migration in the context of sustainable dryland farming development in the Southern Ningxia Hilly Area

The Southern Ningxia Hilly Area is one of the most impoverished areas of Ningxia Hui Autonomous Region(a province)of China due to an economy that mainly relies on agriculture,which is affected by droughts in two out of every three years.Government programs have attempted to develop an increased and sustainable level of scientifically based agricultural production while restoring the environment.However,since the population exceeds the capacity of the land to adequately support it,a program is underway to move 350000 people to more suitable locations.This paper outlines the past improvements to the Southern Ningxia Hilly Area and considers future development in the context of migration for ecological reasons.