THE TIME-COURSE OF PHOTOADAPTATION TO LOW-LIGHT IN PROROCENTRUM MARIAE-LEBOURIAE (DINOPHYCEAE)1

The estuarine dinoflagellate, Prorocentrum mariaelebouriae (Parke & Ballantine 1957) Faust 1974 undergoes increases in pigmentation and photosynthetic efficiency within several days of downward light shifts. These changes can be described by first-order kinetics, as has been reported previously for Chlorophyll (Chl) a in several phytoplankton species. The studies described in this paper were conducted with isolates of populations of Prorocentrum from the Chesapeake Bay. We determined rates of adaptation to low-light for cultures grown at a range of photon flux densities (I₀= 2.65–26.2 E.m^?2, d^?1, shifted to 6.3–7.0% I₀) at three temperatures (10°, 15°, and 20° C), bracketing the conditions this species experiences in situ. In this paper, I report the time-course of changes in α, P_max Chl a, peridinin, and I_k and first-order rate constants, K₁ for changes in α, Chl a and peridinin. cell^?1. K₁ for changes in α cell^?1 averaged 1.58 × 10^?2 h^?1 for conditions encompassing five light treatments and three temperatures; the corresponding mean for Chl a was 1.59 × 10^?2 h^?1. Increases in peridinin measured for five light treatments at 15° C showed a mean K₁ of 1.22 × 10^?2 h^?1, Average percent changes in per cell α, Chl a, and peridinin ranged from 0.4–4.0% h^?1 (10–90% d^?1) following exposure to low-light. Photoadaptive changes are important to Prorocentrum because in nature it occupies turbid waters (K_t≥ 0.5 m^?1) where the mixing depth often exceeds the depth of the photic layer. Cells are entrained beneath a seasonally-stable density discontinuity and are exposed to very low-light (< I E.m^?2.d^?1) for days to weeks during subpycnocline transport. The ability of this species to undergo changes in pigmentation and photosynthetic physiology confers increased efficiency of light harvesting and contributes to this species’survival in the estuary where it is an important component of the dinoflagellate flora.     

Oleic acid transformations by selected strains of Sphingobacterium thalpophilum and Bacillus cereus from composted manure

In a survey of 186 randomly selected microbial strains isolated from composted manure, 63 transformed oleic acid into three types of products: hydroxy fatty acid, fatty amide, and less polar oleyl lipid. Selection of oleic acid-transforming microorganisms was enhanced in nutrient agar supplemented with 0.1% (vol/vol) oleic acid at pH 7.2. Most of the 63 diverse isolates elicited inconsistent and poorly reproduced transformations. However, strains 142b (NRRL B-14797) transformed oleic acid to 10-hydroxystearic acid consistently, and strain 229b (NRRL B-14812) produced an octadecenamide. Taxonomic studies indicated that NRRL strain B-14797, possessing 1,3-dihydroxy-2-amino-15-methylhexadecane and sphinganine bases, was closely related to Sphingobacterium thalpophilum, and NRRL B-14812 was identified as Bacillus cereus.     

Abscisic acid and the accumulation, biological activity and metabolism of four derivatives of [3H]gibberellin A1 in barley aleurone layers

Tritiated GA₁ and four of its synthetic derivatives were studiedin relation to their biological activity, uptake and metabolismby barley aleurone layers. Incubation was done in the presenceand absence of ABA. Tentative identification of some of themetabolites was made by TLC and GLC radiocounting of the metaboliteand its acid hydrolyzed derivative. Only GA₁ promoted -amylase synthesis. Uptake ranged from 20to 42%, varying with the derivative. ABA enhanced uptake of[³H]GA₁ and [³H]pseudoGA₁ and inhibited uptake of [³H]ketoGA₁the Wagner-Meerwein rearrangement product of [³H]GA₁ Uptakeof [³H]GA₁ methyl ester ([³H]GA₁-Me) and [³H]dihydroGA₁ wasunaffected by ABA. [³H]GA₁ was converted to an amphoteric GA₁ derivative ([³H]amphoGA₁)and [³H]GA₁-glycosyl ester. GA₁-Me was metabolized to four products,all of them GA₁ derivatives, including an apparent amphotericGA₁ derivative. DihydroGA₁ was quite stable; only one metabolitewas produced in sufficient yield to analyze. This product didnot cochromatograph with either of the expected acid hydrolyzedepimers of [³H]dihydroGA₁. [³H]ketoGA₁ was readily metabolizedto one product, probably the glycoside. [³H]pseudoGA₁ remainedessentially unmetabolized. Metabolism of all compounds testedwas not dramatically affected by ABA. Surprisingly, no metabolitesfrom hydroxylation at the 2-position were found. ¹ Present address: Monsanto Agricultural Co., 800 N. LindberghBlvd., St. Louis, MO 63166, U.S.A. (Received January 31, 1977; )