Maria Gallo-Meagher

Photosynthetic acclimation of young sweet orange trees to elevated growth CO2 and temperature

Summary Two-year old trees of ‘Ambersweet’ orange, a hybrid of ‘Clementine’ tangerine (Citrus reticulata Blanco) and ‘Orlando’ tangelo (C. paradisi Macf. × C. reticulata), were grown for twenty-nine months under two daytime [CO2] of 360 (ambient) and 720 (elevated) μmol mol−1, and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize the physiology and biochemistry of citrus photosynthesis in response to both elevated [CO2] and temperature, and to test if the photosynthetic capacity of sweet orange, in terms of rubisco activity and protein concentration, was down-regulated under long-term elevated growth [CO2]. Both mature (old) and expanding (new) leaves of trees grown under elevated [CO2] had higher photosynthetic rates, lower transpiration and conductance, and higher water-use efficiency (WUE), compared to those grown under ambient [CO2]. Although leaf WUE was reduced by high temperature, elevated [CO2] compensated for adverse effect of high temperature on leaf WUE. Activity and protein concentration of rubisco were down-regulated in both new and old leaves at elevated [CO2]. In contrast, the amount of total leaf soluble protein was not affected by elevated [CO2] and high temperature. Down-regulation of photosynthetic capacity was greater for the old leaves, although activity and protein concentration of rubisco in the new leaves were higher. Contents of soluble sugars and starch in all leaves sampled, which were higher under elevated [CO2], were generally not affected by high temperature. Within each specific CO2-temperature treatment and leaf type, total soluble sugars remained relatively unchanged throughout the day, as did the starch content of early morning and midday samples, and only a moderate increase in starch for the old leaves at late afternoon sampling was observed. In contrast, starch content in the new leaves increased substantially at late afternoon. Activities of sucrose-P synthase and adenosine 5′-diphosphoglucose pyrophosphorylase were reduced at elevated [CO2] in the old leaves, but not in the new leaves. The photosynthetic acclimation of Ambersweet orange leaves at elevated [CO2] allowed an optimization of nitrogen use by reallocation/redistribution of the nitrogen resources away from rubisco. Thus, in the absence of other environmental stresses, citrus photosynthesis would perform well under rising atmospheric [CO2] and temperature as predicted for this century.

In vitro regeneration of plants from sugarcane seed-derived callus

SummarySugarcane (Saccharum spp. hybrid cv. CP 84-1198) seeds were germinated on modified Murashige and Skoog (MS) basal medium alone or supplemented with 2.3, 4.5, 11.3, 22.5, and 45.0 μM thidiazuron (TDZ), or 4.5, 13.6, 22.6, and 45.0 μM 2,4-dichlorophenoxyacetic acid (2,4-D), or 4.1, 12.4, 20.7, and 41.3, μM picloram. Both auxins delayed seed germination by approximately 5 d. Maximum germination was observed on MS medium supplemented with 45.0 μM TDZ. Callus induction occurred for seed germinated on 2,4-D and picloram-containing media, but not on TDZ medium. The greatest amount of callus (554±198mg per seed) was produced on 4.1 μM picloram. For shoot initiation, calluses were transferred to MS medium alone or supplemented with 2.5 μM TDZ. The highest number of shoots was recorded on TDZ medium from callus that had been obtained originally from media containing either 4.1 or 12.4 μM picloram or 13.6 μM 2,4-D (∼500). All shoots developed roots and grew to maturity on medium with 24,6 μM indolebutyric acid.

Molecular marker screening of peanut ( Arachis hypogaea L.) germplasm for Meloidogyne arenaria resistance

A restriction fragment length polymorphism (RFLP) marker linked to a locus for resistance to Meloidogyne arenaria (Neal) Chitwood race 1, along with visual evaluation following root staining were used to screen four breeding populations and three lines of peanut ( Arachis hypogaea L.) in a root-knot nematode infested field. COAN and Florunner peanut cultivars were used as resistant and susceptible controls, respectively. Genomic DNA was isolated from young leaves of plants during the growing season, and Southern blot analysis was conducted using RFLP probe R2430E. Only COAN and the line TP301-1-8 were homozygous for the resistance marker. During evaluation, root masses were counted and the resistance phenotype scored. This field data confirmed the RFLP marker results. Except for COAN and TP301-1-8, all other genotypes displayed high levels of nematode reproduction. The RFLP probe R2430E provided a useful marker for identifying resistance to the peanut root-knot nematode. Keywords: Arachis hypogaea L., genetics, host resistance, Meloidogyne spp., molecular markers, peanut root-knot nematode. African Journal of Biotechnology , Vol 13(26) 2608-2612