Broad-based resistance to pigeonpea sterility mosaic disease in wild relatives of pigeonpea (Cajanus: Phaseoleae)

Sterility mosaic disease (SMD), an important biotic constraint on pigeonpea (Cajanus cajan) in the Indian subcontinent, is caused by Pigeonpea sterility mosaic virus (PPSMV) transmitted by the eriophyid mite, Aceria cajani. Distinct PPSMV isolates occur in different geographical regions and broad‐based resistance to all these isolates is scarce in cultivated pigeonpea germplasm. Wild relatives of pigeonpea, which are known to possess resistance to several pests and diseases, were evaluated for broad‐based SMD resistance. One hundred and fifteen wild Cajanus accessions from six species (C. albicans, C. platycarpus, C. cajanifolius, C. lineatus, C. scarabaeoides and C. sericeus) were evaluated against three PPSMV isolates prevailing in peninsular India. Evaluations were done under greenhouse conditions in endemic locations of each isolate through mite‐mediated virus inoculation. Fifteen accessions showed resistance to all three isolates: ICP 15614, 15615, 15626, 15684, 15688, 15700, 15701, 15725, 15734, 15736, 15737, 15740, 15924, 15925 and 15926. Most of the wild accessions did not support mite multiplication. The majority of the accessions resistant to PPSMV following inoculations with viruliferous mites were susceptible by graft inoculation, suggesting that vector resistance is conferring resistance to infection with PPSMV. The 15 accessions identified as being resistant to infection to all three virus isolates tested are cross compatible with pigeonpea by traditional breeding. They are therefore useful for exploitation in breeding programmes to increase both the level of SMD resistance and to diversify its genetic base in the cultivated pigeonpea gene pool.     

Change in Levels of Starch and Sugars in Epidermis of Commelina benghalensis during Fusicoccin Stimulated Stomatal Opening

The concentrations of malate, starch and sugars were determinedin presonicated epidermal strips of Commelina benghalensis.During opening, the starch content of epidermis decreased whilethe level of sugars or malate increased. Fusicoccin (FC) stimulatedstomatal opening and elevated the levels of malate and sugars.However, the contribution from sugars was nearly 50% of theosmotic effect of malate and it increased to more than 60% inthe presence of FC. We conclude that FC stimulates stomatalopening by enhancing not only potassium influx into guard cellsbut also hydrolysis of starch into sugars (and malate). Significantcorrelations were noticed between the width of stomatal apertureand epidermal starch (negative), malate and sugars (both positive).The negative relationship between starch and malate or sugarswithin epidermis indicated that starch hydrolysis lead to formationof sugars as well as malate. Starch—sugar interconversioncan therefore play a significant role in modulating the solutepotential of guard cells. Key words: Commelina benghalensis, Stomatal opening, Fusicoccin, Epidermal starch and sugars     

Blue light effects on stomata are mediated by the guard cell plasma membrane redox system distinct from the proton translocating ATPase

Abstract. The effects of blue light on stomata are critically analysed. Blue-light-induced increase in stomatal conductance is preceded by membrane hyperpolarization, proton efflux, potassium uptake and malate synthesis in guard cells. Hypothetically, a flavin containing plasma membrane redox system can pump protons out of guard cells on illumination with blue light. It is proposed that this electrogenic proton pump requires NAD(P)H but does not involve ATP/ATPase.     

The role of larval nutrition in pre-imaginal biasing of caste in the primitively eusocial wasp Ropalidia marginata (Hymenoptera: Vespidae)

Abstract.

• 1 When freshly eclosed females of the primitively eusocial wasp Ropalidia marginata (Lep.) are isolated, only about 50% of them build nests and lay eggs thereby suggesting a pre-imaginal biasing of caste.
• 2 Wasps that lay eggs take a very variable amount of time after eclosion to start doing so.
• 3 Females eclosing from nests where larvae are fed at a relatively higher rate are more likely to become egg-layers and are likely to take less time after eclosion to begin to lay eggs.
• 4 Thus, both forms of pre-imaginal biasing of caste, namely, differences in egg laying capacity and differences in the time taken to attain reproductive maturity, appear to be influenced by larval nutrition.

     

Variation with age in the photosynthetic carbon fixation pattern by leaves of Amaranthus paniculatus and Oryza sativa: Change in the primary carboxylation but no shift from C4 or C3 pathway

Abstract The pattern of photosynthetic carbon fixation by leaves of Amaranthus paniculatus L. (a C₄ plant) and Oryza sativa L. (a C₃ plant) varied with age. Younger leaves of A. paniculatus incorporated ¹⁴CO₂ into malate and aspartate while senescent leaves fixed predominantly into phosphoglycerate (PGA) and sugar phosphates. Only developing leaves of O. sativa formed malate/aspartate whereas mature and senescent leaves produced PGA/sugar phosphates as the initial labelled products. Correspondingly the ratio of phosphoenolpyruvate/ribulose bisphosphate (RuBP) carboxylase activities was higher in younger leaves of A. paniculatus and developing leaves of O. sativa than in older leaves. However, pulse chase experiments revealed that the main donors of carbon to end products, irrespective of leaf stage, were C₄ acids and PGA in A. paniculatus and O. sativa respectively. The results suggest that although an apparent change from initial β-carboxylation to RuBP carboxylation occurs during leaf ontogeny in both the plants, the overall leaf photosynthesis remains C₄ or C₃. The high rate of ¹⁴CO₂ incorporation into PGA/sugar phosphates by senescent leaves of A. paniculatus is suggested to be partly due to the increased intercellular spaces in their mesophyll, allowing greater access of CO₂ directly to RuBP carboxylase in the bundle sheath.     

Isolation and characterization of microsatellite markers from malaria vector,Anopheles culicifacies

Anopheles culicifacies, an important vector in the Indian subcontinent is a complex of five sibling species of which four are vectors. We describe the isolation of 31 microsatellite markers from the recently recognized isomorphic species A of which 13 were characterized in sympatric populations of Anopheles culicifacies isomorphic species A and B. The allele frequencies ranges from two to 12 in species A and two to seven in species B. Species A being a vector, and that these markers can be used in closely related species, makes the isolation of these markers important to study population structure of all sibling species in this complex.     

Inhibition of photosynthesis by osmotic stress in pea (Pisum sativum) mesophyll protoplasts is intensified by chilling or photoinhibitory light; intriguing responses of respiration

The effects of reduced osmotic potential on photosynthesis and respiration were studied in mesophyll protoplasts of pea (Pisum sativum). Osmotic stress was induced by increasing the sorbitol concentration in the medium from 0·4 kmol m⁻³ (-1·3 MPa) to 1·0 kmol m⁻³ (-3·1 MPa). Protoplasts lost up to 35% of the maximum capacity of photo-synthetic carbon assimilation (but not PS II mediated activity) soon after exposure to 1·0 kmol m⁻³ sorbitol. The response of protoplast respiration to osmotic stress was intriguing. Respiration was stimulated if stress was induced at 25°C, but was inhibited when protoplasts were subjected to osmotic stress at 0°C. Photosynthesis was also much more sensitive to osmotic stress at 0°C than at 25°C. The inhibitory effects of osmotic stress on photosynthesis as well as respiration were amplified by not only chilling but also photoinhibitory light. The photosynthetic or respiratory activities of protoplasts recovered remarkably when they were transferred from hyperosmotic (1·0 kmol m⁻³ sorbitol) back to iso-osmotic medium (0·4 kmol m⁻³ sorbitol), demonstrating the reversibility of osmotic-stress-induced changes in protoplasts. Respiration was more resistant to osmotic stress and was quicker to recover than photosynthesis. We suggest that the experimental system of protoplasts can be useful in studying the effects of osmotic stress on plant tissues.     

Antitranspirant Activity of Inhibitors of Cyclic Photophosphorylation

The antitranspirant activity of three inhibitors of cyclic photophosphorylation(2,4-dinitro-phenol, 2-chloromercuri-4,6-dinitrophenol, andsalicylaldoxime) on 6-week-old plants of Datura arborea wasexamined. The test compounds reduced transpiration and the effectpersisted for 12 d. The dry matter production by the plantswas not affected. The reduction in water loss was caused bystomatal closure. Inhibitors of cyclic photophosphorylation,by virtue of their prolonged action associated with a smalleffect on dry matter accumulation, may be useful as antitranspirants.