Suboptimal temperatures cause grain yield reductions generally associated with low seed-set in sorghum [Sorghum bicolor (L.) Moench]. Low proline concentration in pollen has been associated with cold-induced male sterility. This study was done to (i) determine free proline concentrations in grain sorghum pollen after low temperature exposure, (ii) determine the relationship between seed-set and proline concentration in pollen, and (iii) determine the association of proline concentration in pollen with grain yield in sorghums of different maturity. Eleven sorghum genotypes, grown in a greenhouse at 27/22 °C (day/night) until the early boot stage were transferred to 20/10 °C in growth chamber until physiological maturity. Concentration of proline in pollen was determined at anthesis and related to seed number and grain yield. Proline concentrations in pollen increased from 19 to 36 μg∙mg−1 fresh wt. to 30 to 49 μg∙mg−1 fresh wt. at low temperatures. Seed number and grain yield were reduced by low temperature in most of the genotypes. Percent seed-set in male sterile lines was significantly correlated (r = 0.45**) with free proline concentrations in the pollen from 13 fertile hybrids grown under cold or control conditions. Higher concentrations of proline in pollen under cool and also control temperatures seemingly contribute to greater pollen viability in grain sorghum. In 21 sorghum hybrids grown under control temperatures, seed number per panicle was found correlated (r = 0.42*) to free proline concentrations in pollen. Genotypic differences in pollen proline concentration were not associated with differences between maturity groups. Keywords: Sorghum bicolor (L.) Moench, pollen, free proline, low temperatures, seed-set, grain yield.

The selection of adequate plant species is a prerequisite for cleaning-up contaminated soils by means of phytoextraction which is a time and cost-effective technology. Here first results of the screening of plant species from three different mining areas in South America are reported: A copper mine in Peru ("Mina Turmalina"), a silver mine in Ecuador ("Mina San Bartolomé") and a copper mine in Chile ("Mina El Teniente"). The accumulation of heavy metals and As in shoots as a function of extractable metal concentrations in the soils was analyzed in field samples. The different plant species collected on the severely polluted soils exhibited large differences in shoot accumulation of heavy metals and As. Among the grass species (Poaceae), the highest shoot As concentrations were found in Paspalum sp. (> 1.000 µg/g) and Eriochloa ramosa (460 µg/g) from the Cu mine in Peru, and in Holcus lanatus and Pennisetum clandestinum (> 200 µg/g) from the silver mine in Ecuador. Paspalum racemosum also accumulated considerable concentrations of Cu and Zn. The species from the genus Bidens (Asteraceae) were able not only to accumulate high shoot As concentrations (> 1000 µg/g in B. cynapiifolia from Peru), but also considerable amounts of Pb (B. humilis from Chile). The highest Cu shoot concentrations were found in Mullinum spinosum (870 µg/g) and in B. cynapiifolia (620 µg/g). The shoot accumulation of Zn was highest in Baccharis amdatensis (> 1900 µg/g) and in Rumex crispus (1300 µg/g) from the silver mine in Ecuador. The potential usefulness of these species for phytoremediation technologies is discussed.

Previous studies have demonstrated that pollen of sorghum [Sorghum bicolor (L.) Moench] loses capacity to both germinate in vitro and to set seed in vivo soon after being shed. The current study evaluates the capacity for dehydrated pollen to effect in vitro germination, reduce tetrazolium chloride, and set seed on cytoplasmic male sterile plants. Morphological changes during pollen germination were examined by scanning electron microscopy (SEM). Close to 70 % of the pollen germinated in 5 min, or less, when collected at 80 % relative humidity (RH) and stored in sealed glass vials. Pollen tubes elongated autotropically with atmospheric humidity apparently being a controlling factor in the process. Pollen dehydrated at 50% RH and 25 degrees C for 15-30 min neither germinated in vitro, reduced tetrazolium chloride, nor set seed on male sterile plants. Rehydrating the pollen did not restore the capacity for germination. SEM micrographs demonstrated that elongating pollen tubes encircled the pollen grain and were contiguous to the surface. A fibrillar-like material existed on the exine of separated pollen grains at the point where the grains had been previously attached.

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