Phenylalanine ammonia lyase (PAL) catalyzes the nonoxidative deamination of l-phenylalanine to form trans-cinnamic acid and a free ammonium ion. It plays a major role in the catabolism of l-phenylalanine. The presence of PAL has been reported in diverse plants, some fungi, Streptomyces and few Cyanobacteria. In the past two decades, PAL has gained considerable significance in several clinical, industrial and biotechnological applications. Since its discovery, much knowledge has been gathered with reference to the enzyme's importance in phenyl propanoid pathway of plants. In contrast, there is little knowledge about microbial PAL. Furthermore, the commercial source of the enzyme has been mainly obtained from the fungi. This study focuses on the recent advances on the physiological role of microbial PAL and the improvements of PAL biotechnological production both from our laboratory and many others as well as the latest advances on the new applications of microbial PAL.

Main conclusionEffects 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.

Drought is an important factor which limits growth of sugarcane. To elucidate the physiological and biochemical mechanisms of tolerance, a pot experiment was conducted at Sugarcane Research Institute, Kaiyuan, China. Two genotypes (Yuetang 93-159-sensitive and Yunzhe 05-51-tolerant), were subjected to three treatments; 70±5% (control), 50±5% (moderate drought) and 30±5% (severe drought) of soil field capacity. The results demonstrated that drought induced considerable decline in morpho-physiological, biochemical and anatomical parameters of both genotypes, with more pronounced detrimental effects on Yuetang 93-159 than on Yunzhe 05-51. Yunzhe 05-51 exhibited more tolerance by showing higher dry biomass, photosynthesis and antioxidant enzyme activities. Compared with Yuetang 93-159, Yunzhe 05-51 exhibited higher soluble sugar, soluble protein and proline contents under stress. Yunzhe 05-51 illustrated comparatively well-composed chloroplast structure under drought stress. It is concluded that the tolerance of Yunzhe 05-51 was attributed to improved antioxidant activities, osmolyte accumulation and enhanced photosynthesis. These findings may provide valuable information for future studies on molecular mechanism of tolerance.

The relationship between endogenous ethylene production and natural defoliation rate was examined in sugarcane cultivars with different natural defoliation traits. Ethylene production was examined at different positions on leaf sheaths and leaf scars at various sugarcane maturation stages using gas chromatography as an external standard method. During the sugarcane maturation process, ethylene production was greatest in the 2nd leaf sheath scar, followed by the 5th and 10th, in that order. It was also greatest during the early maturation stage, followed by the mid-maturation and harvest stages. Ethylene production of the leaf sheaths and leaf scars differed significantly among the sugarcane cultivars. Cultivars that defoliate easily produced significantly more ethylene than those that do not defoliate easily. The natural defoliation rates was greatest in the harvest stage, followed by mid-maturation and early maturation stage. Correlation analysis indicated that ethylene production was positively correlated with natural defoliation rates, particularly during early-and mid-maturation stages.

The relationship between natural defoliation rate and endogenous ethylene, indole-3-acetic acid (IAA), and abscisic acid (ABA) levels in four sugarcane cultivars possessing different defoliation traits was investigated. Leaf sheath, leaf scar, and leaf blade samples were collected from the 10th leaf position below the fully expanded leaves during sugarcane maturation stage. Ethylene, IAA, and ABA levels were measured using gas chromatograph, liquid chromatograph, and external standard methods. The results showed that during sugarcane maturation, the highest natural defoliation rate was observed in CYZ03-194, followed by CYZ01-1413, CMT02-467, and CYA99-91. Ethylene production and IAA levels in the leaf scars, leaf sheaths, and leaf blades were the highest during the early-to-mid-maturation stage and decreased afterwards. The ABA levels showed a mono-peak curve change and peaked at the late-to-mid-maturation stage. Ethylene production in leaf scars during the early-to-mid-and midmaturation stages as well as ABA levels in leaf scars at the late-to-mid-maturation stage significantly differed among the cultivars, with the highest levels in CYZ03-194, followed by CYZ01-1413, CMT02-467, and CYA99-91. On the other hand, the IAA levels in leaf scars and leaf sheaths at the early-to-mid-maturation stage were highest in CYA99-91, followed by CMT02-467, CYZ01-1413, and CYZ03-194. Correlation analysis demonstrated a positive correlation between the natural defoliation rate and ethylene production, ABA level, ethylene/IAA ratios, and ABA/IAA ratios, whereas a negative correlation was observed with IAA level during the early-to-mid-and midmaturation stages.