Main conclusion Effects of a low aluminum (Al) dose were characterized. The Al supplement inhibited root growth but enhanced leaf growth in maize lines with different Al sensitivities. High levels of Al are phytotoxic especially in acidic soils. The beneficial effects of low Al levels have been reported in some plant species, but not in maize. Maize is relatively more sensitive to Al toxicity than other cereals. Seedlings, at the three leaf stage, of four Chinese maize foundation parent inbred lines with different Al tolerances, were exposed to complete Hoagland’s nutrient solution at pH 4.5 supplemented with 48 μM Al³⁺ under controlled growth conditions, and then the Al stress (AS) was removed. The leaf and root growth, root cell viability, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ions (K⁺, Ca⁺⁺ and Mg⁺⁺), photosynthetic rate and chlorophyll, protein and malondialdehyde contents in tissues were assayed. In conclusion, a low Al dose inhibits root growth but enhances leaf growth in maize. The Al-promoted leaf growth is likely a result of increased protein synthesis, a lowered Ca⁺⁺ level, and the discharge of the growth-inhibitory factors. The Al-promoted leaf growth may be a ‘memory’ effect caused by the earlier AS in maize. Al causes cell wall rupture, and a loss of K⁺, Ca⁺⁺ and Mg⁺⁺ from root cells. CAT is an auxiliary antioxidant enzyme that works selectively with either SOD or POD against AS-related peroxidation, depending on the maize tissue. CAT is a major antioxidant enzyme responsible for root growth, but SOD is important for leaf growth during AS and after its removal. Our results contribute to understanding how low levels of Al affect maize and Al-resistant mechanisms in maize.

We studied the transcriptional profiles of leaves and roots of three-leaf stage seedlings of the maize inbred line YQ7-96 under conditions of salt stress (100 mM NaCl) and removal of salt stress (RSS). A total of 296 genes were regulated specifically by the stress, of which 206 were specific to leaves and 90 were specific to roots. Stress-regulated genes were classified into eight and seven expression patterns for leaves and roots, respectively. There were 60 genes which were regulated specifically by RSS, 27 of which were specific to leaves and 33 specific to roots. No genes were found to be co-regulated in tissues and to be regulated commonly by the stress and RSS. It can be concluded that (i) at the early stage of the stress, transcriptional responses are directed at water deficit in maize leaves but at both water deficit and Na⁺ accumulation in roots; (ii) at the later stage, the responses in leaves and roots result from dual effects of both water deficit and Na⁺ accumulation; (iii) the polyamine metabolic pathway is an important linker for the co-ordination between leaves and roots to accomplish the tolerance of the whole maize plant to the stress; (iv) the stress can lead to genomic restructuring and nuclear transport in maize; (v) maize leaves are distinct from roots in terms of molecular mechanisms for responses to and growth recovery from the stress; and (vi) mechanisms for the maize responses to the stress differ from those for their growth recovery during RSS.

The biomass of filamentous fungi is an important cost-effective biomass for heavy metal biosorption. However, use of free fungal cells can cause difficulties in the separation of biomass from the effluent. In this study, we immobilized the living conidia of the heavy metal-resistant Penicillium janthinillum strain GXCR by polyvinyl alcohol (PVA)-sodium alginate (SA) beads to remove heavy metals from an aqueous solution containing a low concentration (70 mg/L) of Cu, Pb, and Cd. The PVA-SA-conidia beads showed perfect characters of appropriate mechanical strength suitable for metal removal from the dynamic wastewater environment, an ideal settleability, easy separation from the solution, and a high metal biosorption and removal rate even after four cycles of successive sorption-desorption of the beads, overcoming disadvantages when fungal biomasses alone are used for heavy metal removal from wastewater. We also discuss the major biosorption-affecting factors, biosorption models, and biosorption mechanisms.

Cassava (Manihot esculenta) is valued mainly for high content starch in its roots. Our understanding of mechanisms promoting high starch accumulation in the roots is, however, still very limited. Two field-grown cassava cultivars, Huanan 124(H124) with low root starch and Fuxuan 01(F01) with high root starch, were characterised comparatively at four main growth stages. Changes in key sugars in the leaves, stems and roots seemed not to be strongly associated with the final amount of starch accumulated in the roots. However, when compared with H124, F01 exhibited a more compact arrangement of xylem vascular bundles in the leaf axils, much less callose around the phloem sieve plates in the stems, higher starch synthesis-related enzymatic activity but lower amylase activity in the roots, more significantly up-regulated expression of related genes and a much higher stem flow rate (SFR). In conclusion, higher starch accumulation in the roots results from the concurrent effects of powerful stem transport capacity highlighted by higher SFR, high starch synthesis but low starch degradation in the roots and high expression of sugar transporter genes in the stems. A model of high starch accumulation in cassava roots was therefore proposed and discussed.