Potassium requirement of pyruvate kinase extracted from leaves of halophytes

Pyruvate kinase enzymes were partially purified from leaves of halophytes, Atriplex gmelini C. A. Mey., Chenopodium acuminatum Wild, and Spergularia salina J. et C. Presl., grown hydroponically in the presence of 250 m M NaCl in a greenhouse, to determine their K_m values for potassium. The values were all ca 10⁻³ M , as also reported for the glycophyte enzymes. However, the K_m values were reduced by 60 to 70% by the addition of betaine to a concentration of 1 M .     

Ultrastructural alterations to chloroplasts in triazine-resistant weed biotypes

Ultrastructural, morphometric and physiological techniques were used to determine the consistent chloroplast differences between triazine-resistant (R) and triazine-susceptible (S) biotypes of Amaranthus hybridus L., Chenopodium album L., and Brassica campestris L. All R biotypes had a larger proportion of the chloroplast volume as grana lamellae and a lower proportion of starch and stroma lamellae than S biotypes. In the R biotypes, a greater percentage of grana contain larger numbers of thylakoids per granum. A greater proportion of chlorophyll associated with the light-harvesting chlorophyll alb protein and a lower chlorophyll alb ratio, traits associated with an increase in grana lamellae, were noted in R biotypes. Chloroplasts of S biotypes could be modified to ultrastructural phenocopies of those in R biotypes by treatment with sublethal levels of the PSII inhibiting herbicides, bentazon, diuron, atrazine and prometon. Despite the structural similarities to R biotypes, the modified S biotypes were not resistant to atrazine as determined by fluorescence measurements. Thus, the structural alterations observed are apparently secondary effects of impaired photosynthetic electron transport in R biotypes, and are not the cause of triazine resistance.     

Photosynthetic activity and chloroplast structural characteristics in triazine-resistant biotypes of three weed species

Triazine-resistant (R) and susceptible (S) biotypes of Chenopodium album, Conyza bonaeriensis and Setaria glauca were compared in terms of photosynthetic activity, chloroplast ultrastructure, and polar-lipid composition of thylakoid membranes. Concerning photosynthetic activity, R relative to S biotypes showed lower rates in photosystem II electron transport (R/S ratios in the 0.3-0.5 range), which were correlated with increases in the ratio of I to P levels of the fluorescence emission curve, but similar rates in both whole-chain electron transport by thylakoids and photosynthetic oxygen evolution at different light intensities and at temperatures of 20 and 30°C by leaf discs. Concerning chloroplast structural characteristics, R and S biotypes did not show differences in degree of thylakoid appression and chlorophyll a/b ratio. However, thylakoid polar-lipids of R biotypes exhibited a higher degree of unsaturation, specially, in its monogalactosyl diglyceride fraction; they were richer in trans-hexadecenoic acid in its phospholipid fraction and they had higher contents in monoglactosyl diglyceride. The above results are discussed in relation to possible differences in photosynthetic performance between R and S plants.     

No effect of larval experience on adult host preferences in Polygonia c‐album (Lepidoptera: Nymphalidae): on the persistence of Hopkins’ host selection principle

Abstract 1. The possible effect of juvenile imprinting or ‘chemical legacy’ on the subsequent oviposition – often called the ‘Hopkins’ host selection principle’– has been a controversial but recurrent theme in the literature on host‐plant preference. While it appears possible in principle, experimental support for the hypothesis is equivocal. The present study points out that it is also important to consider its theoretical implications, and asks under what circumstances, if any, it should be favoured by natural selection. 2. Following this reasoning, it is predicted that host preference in the polyphagous butterfly Polygonia c‐album L. (Lepidoptera, Nymphalidae) should not be influenced by larval environment. This was tested by rearing larvae on three natural host plants: the high‐ranked Urtica dioica and the medium‐ranked Salix cinerea and Ribes uva‐crispa, and exposing the naive females to oviposition choices involving the same set of plants. 3. It was found that larval host plant had no effect on oviposition decisions of the adult female. Hence, the Hopkins’ host selection principle does not seem to be applicable in this species. 4. Based on recent insights on how accuracy of environmental versus genetic information should affect the control of developmental switches, the conditions that could favour the use of juvenile cues in oviposition decisions are discussed. Although the Hopkins’ host selection hypothesis cannot be completely ruled out, we argue that the circumstances required for it to be adaptive are so specific that it should not be invoked as a general hypothesis for host selection in plant‐feeding insects.     

橄榄北移试验初报

在广西桂林引种橄榄已能正常开花结果,种子能繁殖后代．后代植株也能正常开花结果．橄榄北移试种获得成功。     

Isozyme profiles associated with the hypersensitive response of Chenopodium foetidum to plum pox virus infection

Isozyme profiles of esterases (E.C. 3.1.1.1), glutamate oxaloacetate transaminase (E.C. 2.6.1.1) and peroxidases (E.C. 1.11.1.7) have been determined in healthy tissues of Chenopodium foetidum as well as their modifications during leaf development. The effect of plum pox virus infection on the isozyme profiles has also been studied. Virus-induced necrotic lesions displayed a peroxidase (POX) pattern that has not been found in any other tissue of the plant so far analyzed. The pattern was similar to that of old yellow leaves, except that POX-B, which was detected in the necrotic lesions, has not been detected in any developmental stage of healthy leaves. Changes in the peroxidase profile seem to begin early during infection, even before necrosis is visible. We suggest that senescence is established at necrotic lesions extending from there to the rest of the infected leaf affecting the peroxidase isozyme pattern. However, other changes, which induce POX-B, must also take place at necrotic lesions. These do not extend to the rest of the infected leaves. Plum pox virus infection has less effect on the glutamate oxaloacetate transaminase and esterase isozyme patterns, inducing an almost normal senescence pattern.     

Effect of light environment during soil disturbance on germination and emergence pattern of weeds

This paper describes results from experiments which investigated the effects of light intensity during soil disturbance on germination and emergence pattern of weeds. Different emergence patterns were demonstrated for seeds which are instantly flash induced compared to seeds which are induced to germinate by integrating a weak light signal over a period of time. A reduced and delayed emergence is achieved after a disturbance in darkness compared to a soil disturbance in daylight. The increased emergence after soil disturbance in daylight is due to additional plants originating from seeds placed at a soil depth in the pots where daylight cannot penetrate and induce seeds to germinate, but which are induced during the short exposure period. A close relationship between soil disturbance intensity and number of weed plants emerging was found in field experiments with shallow harrowings. It was also shown that a portion of the increased number of seedlings arising when soil disturbance is carried out in daylight, compared to soil cultivation in darkness, originates from seeds germinating from deeper soil layers, resulting in a deeper average germination depth.     

Evidence of Dichogamy in Santalum album L.

Flowering, fruit set, embryological development, and pollination trials were Investigated In Santslum album L. Each ovary may have three to four ovules. Mlcrosporogenesls and megasporogenesls In the same flower were synchronized at the earlier stages of flower development. However, at anthesls, when pollen was mature, the magaspore had developed only to the stage of a one- to two-nucleus embryo sac. As the eight-nucleus embryo sac developed, some mamelon cells began to undergo programmed cell death, forming holes Into which the eight-nucleus embryo sacs extended, becoming ＂N＂ or ＂S＂ shaped. The development from a two-nucleus embryo sac to a matured eight-nucleus embryo sac lasted up to 10 d. Fruit-set from open pollination was less than 2%. The endosperm develops prior to division of the zygotic embryo and one to three embryos and endosperms were formed In the same fruit. A mature seed usually germinates to produce one seedling; however, two and three seedlings from one seed were also observed, albeit at a low frequency. Pollination trials showed that no seed sets when Inflorescences were covered with s bag; however, artificial pollination could Improve fruit set. Our pollinaUon trials and embryological studies proved that the flower of S. album Is dlchogamous and fruit set has high heterozygosity.     

Sixty-Five Years of Searching for the Signals That Trigger Flowering

This review summarizes the long-term research of photoperiodic flower induction in two Chenopodium species, one of which, C. rubrum, is a short-day plant, while the other, C. murale, is a long-day plant. In the course of purification of florigenic extracts inducing flowering in C. rubrum plants kept under noninductive photoperiodic conditions, we did not succeed in identifying its active component(s). During the inductive treatment, the phloem transport of cytokinins was enhanced and their content in the shoot apex greatly increased for some time. The review also summarizes the results of the application of direct electric current to the leaves of C. rubrum plants. This treatment interferes with the transport of some active signal(s) from leaves to the apex, resulting in the inhibition of flowering induction. The problem of the rhythmicity of flowering in C. rubrum plants was considered, particularly, the possibility of melatonin (N-acetyl-5-methoxytryptamin) participation in photoperiodic induction. Melatonin accumulation in darkness appears to determine the amplitude of the flowering rhythm but not its phase or period.