Pipecolic acid induces free radicals and is dependent on SA and G3P for its de novo synthesis in distal leaves.

Summary The study objectives were to identify the horizontal and vertical distributions of adult Chinese sturgeon (Acipenser sinensis) in relation to the Habitat Suitability Index (HSI) in order to assess the utility of the only remaining spawning grounds by adults and to understand the effects of river alterations on habitat use. Twenty‐five adults were surgically implanted with ultrasonic transmitters and located by mobile tracking and fixed monitoring stations during the 2006–2009 spawning seasons. Fish locations and depths along with water depth and bottom characteristics (topography, velocity, and embeddedness) were measured during tracking and used to determine HSI curves for non‐spawning and spawning adults. Most fish locations (91%) were on the spawning grounds (GZD to Miaozui reaches). Horizontal distribution differed before and after spawning, among years, and between the sexes. Adults used deeper depths during the day than at night (P < 0.001), while also preferring shallower depths on the day of spawning rather than the days before and after. Mature females used deeper water than other females (P < 0.001). Comparison of horizontal and vertical distributions before and after river alterations found fewer adults using the grounds impacted by a diversion dike which was built on the spawning grounds. Adults also used shallower depths after the Three Gorges Dam regulated river flow over the spawning grounds. The HSI model and the use of Weighed Usable Areas (WUA) for mature and immature adults indicated suitable habitat was available, but was reduced by the river alterations resulting in reduced spawning success and placing the population into a situation close to extirpation.

A 56-days growth trail was conducted to determine the dietary phosphorus requirement for young Siberian sturgeon Acipenser baerii. In total 495 healthy young Acipenser baerii weighed average 14.50 ± 1.00 g were selected and randomly distributed into 33 tanks (eleven treatments with triplicates each). The growth performance of Acipenser baerii improved significantly with the level of phosphorus increasing, weight gain rate arrived at 431.94% for the maximum while the phosphorus level up to 0.60%. Ash and phosphorus content of whole fish increased with the level of phosphorus in the diet and remained stable while dietary phosphorus was more than 0.99% (P > 0.05). There were positive correlations between ash, calcium and phosphorus content in scutae and the dietary phosphorus had offered. Plasma calcium, plasma phosphorus content and alkaline phosphatase activity were influenced significantly by dietary phosphorus levels (P < 0.05). Based on WGR and phosphorus content in whole fish presented in this report, we would suggest a value of 0.50-0.87% phosphorus be used in formulated sturgeon feed.

Characteristics of bottom substrates have caused wide concernas to their importance for sturgeon spawning ground requirements. Substrate requirements for spawning of Chinese sturgeon Acipenser sinensis have not yet been well studied because of the difficulties in investigating on a large and fast flowing river such as the Yangtze River. During 2007 and 2008, the underwater video surveys on the present spawning ground of A. sinensis were successfully conducted. Two kinds of substrates were documented: one stable infrastructure consisting of large boulders and cobbles mixed with pebbles and gravels, the other comprise sediments in transportation, especially coarse and fine sands. The large boulders (size range 20-50 cm), cobbles and pebbles (size range 10-20 cm), pebbles or gravels are estimated to account for 50, 30, 20% of the available substrates of the infrastructure on spawning ground according to our underwater video survey points, respectively. The transporting sands can be observed in most area, while the river sand embedded or covered the large structural compounds just occur in certain area and the substrate where spawning occurs annually and occasionally were similarly ÔcleanÕ of fine sediment. The eggs (embryos) of Chinese sturgeon have been observed ÔhidingÕ in or adhering to the interstitial spaces between the clean large materials e.g. boulders, cobbles and pebbles during the 2007 ⁄ 2008 study period. Therefore the degree of cover of the larger particles by sand (embeddedness), which will directly affect the spawning habitat and subsequently influence survival of the new hatched larvae, were assessed by determining the topographic data in relation to water velocity. The multivariable correlation analysis and binary logistic regression analysis showed that the comparably topographic characteristics which had been confirmed to be suitable at the historic and present spawning sites would eventually contribute to the substrate deposition. The embeddedness of the sediment are obviously lower in shallow water with higher water velocity than in the deeper water with slower water current (P < 0.01) and the sites where the embryo occur can be predicted with the three physical variables: embeddedness of the sediment, water velocity and river bottom elevation. The bedform morphology with an adverse slope (channel slope adverse to the bottom elevation grads) formed by larger blocks of substrate, will improve the water turbulence at high current to carry the suspended or embedded fine sediments away from the spawning site and (in turn) provide enough interstitial spaces for effective egg deposition and incubation. Therefore the substrate requirements for the spawning habitat of Chinese sturgeon should be described and assessed more than just rocky and gravelly substrate, taking the embeddedness of sediment in well consider. The concepts of detailed description of the substrate requirements and their relationship with the overall bedform morphology has been shown to be essential to provide benefit for the rehabili...