C4 photosynthetic modifications in the evolutionary transition from land to water in aquatic grasses

Cladistic analysis supports the conclusion that the Orcuttieae tribe of C₄ grasses reflect evolution from a terrestrial ancestry into seasonal pools. All nine species in the tribe exhibit adaptations to the aquatic environment, evident in the structural characteristics of the juvenile foliage, which persist submerged for 1–3 months prior to metamorphosis to the terrestrial foliage. Aquatic leaves of the least derived or basal genus Neostapfia have few morphological and anatomical characteristics specialized to the aquatic environment and have retained full expression of the C₄ pathway, including Kranz anatomy. Orcuttia species have many derived characteristics and are more specialized to the aquatic environment. These latter species germinate earlier in the season and persist in the submerged stage longer than Neostapfia and evidence from the literature indicates length of submergence is positively correlated with fitness components. Aquatic leaves of Orcuttia species lack Kranz or PCR bundle sheath anatomy, yet ¹⁴C-pulse chase studies indicate >95% malate + aspartate as the initial products of photosynthesis and these products turn over rapidly to phosphorylated sugars, indicating a tight coupling of the C₄ and C₃ cycles. Presence of the C₄ pathway is further supported by enzymological data. Contemporary dogma that Kranz anatomy is a sine qua non for operation of the C₄ pathway is contradicted by the patterns in Orcuttia; however, it is unknown whether the pathway acts as a CO₂ concentrating mechanism in these aquatic plants. Received: 12 June 1997 / Accepted: 10 February 1997     

Neuroendocrine deficiency effects on trophic metabolism and water balance in the cockroach, Blaberus discoidalis

Unoperated, sham-operated (SO) and allatectomized (CA⁻) adult, male Blaberus discoidalis lost ca. 300 mg of live weight (LW) during the first 10 days after ecdysis. This decrease resulted from losses in both dry weight (DW) and water. An additional 100 mg LW loss was found in allatectomized-cardiacectomized (CA⁻+CC⁻) animals as a result of increased water loss.The LWs of operated and unoperated controls remained nearly constant between 10 and 30 days of age as DW increased and water decreased in comparable amounts. However, the LW of 30-day-old CA⁻+CC⁻ animals was 100 mg greater than the controls due to increased water retention.Compared to controls, food consumption and faecal production were reduced by 50 per cent in CA⁻ and CA⁻+CC⁻animals, but the percentage of food digested was unchanged. Efficiency of converting food to DW in CA⁻+CC⁻animals was twice that of SO and CA⁻ animals and four times that of the unoperated controls.These results indicate that extirpation of the retrocerebral complex decreases food intake but not digestion. Nutrient storage or conversion to body matter is apparently enhanced by neuroendocrine deficiency. Therefore, a gross nutritional deficiency is unlikely in CA⁻+CC⁻animals.The LW changes occurring after neuroendocrine deficiency were related to changes in water content. DW changes were comparable in all control and experimental groups. The results indicate both diuretic and antidiuretic effects by the neuroendocrine system depending on the age of the animals.     

Endocrine regulations of ovarian maturation in the cockroach Blaberus discoidalis

The first gonotrophic cycle of oocyte maturation was defined for virgin Blaberus discoidalis cockroaches. A high correlation was found between growth of the basal oocytes and increased ovarian protein content. Allatectomy blocked ovarian protein formation, whereas JH-III administration compensated for the loss of the corpora allata. Experiments involving neuro-endocrine surgery and hormone replacement therapy indicated that JH, alone, could stimulate ovarian protein formation; however, the addition of neuroendocrine extracts enhanced the JH effects. The data suggest that both JH and neurohormones stimulate aspects of ovarian protein formation in this insect.     

POST-FIRE REGENERATION OF SOUTHERN CALIFORNIA CHAPARRAL

Succession of chaparral shrubs was studied for the first 4 years after fire on the four major slope faces at three elevations in southern California. Although total cover fluctuated from year to year, shrub cover increased annually through the third year. There was little or no increase in shrub cover between the third and fourth years. Four years after fire the shrubs covered 55% ground surface at the highest elevation site but only 28% at the lowest elevation site. Shrub cover was similar between slope faces with one exception; at the lowest elevation site shrub cover was twice as great on the north and east-facing slopes as on the south and west-facing slopes. Post-fire recovery of shrubs was by seedlings and/or resprouts. Yucca whipplei was an exception in that it did not resprout once the aboveground parts were killed nor did seedlings establish after fire, however the aboveground parts of many Y. whipplei survived the fire. Species which reproduced entirely by seed did so in the first post-fire year from soil-stored seed with the exception of Ceanothus greggii at the highest elevation site. This species was entirely absent the first year after fire but abundant in the second year. Species producing both resprouts and seedlings varied from site to site in the proportion of resprouts:seedlings. Between 83–100% of the post-fire populations of Cercocarpus betuloides, Arctostaphylos glandulosa, and Xylococcus bicolor were resprouts whereas 12–13% of Ceanothus tomentosus were resprouts. For Adenostoma fasciculatum, resprouts constituted 27–54% of the population at the lowest elevation and 65–94% at the highest elevation; whereas, the Quercus dumosa population was 100% resprouts at the lowest elevation and 31–67% resprouts at the highest elevation. Data are presented on the height of resprouts and seedlings for all species at the end of the first post-fire year.