THE FINE STRUCTURE OF SPOROGENESIS IN THE XANTHOPHYCEAN ALGA PSEUDOBUMILLERIOPSIS PYRENOIDOSA1,2

The fine structure of vegetative cells, sporogenesis, and zoospores of the xanthophycean alga Pseudo-bumilleriopsis pyrenoidosa is described. Cleavage in sporogenesis closely resembles that of certain aquatic fungi.     

鸡的缝匠肌中的慢肌纤维在切断神经后所发生肥大的长期性和内部结构的观察

鸡的缝匠肌是含有Ⅰ型(慢)纤维和Ⅱ型(快)纤维的混合肌,在该肌的神经被切断并阻止其再生后1、4与6个月进行观察。冰冻切片结合肌原纤维三磷酸腺苷酶(m-ATP-ase)的染色法显示慢肌纤维发生成倍的肥大。在去神经6个月后快、慢纤维仍然因酸或碱性预处理而呈现染色的反转。在电镜下观察,去神经后发生肥大的慢纤维仍然呈现微丝的正常排列。清楚的A、Ⅰ带与 H 带。它的 Z 线清楚但在有些纤维中的有些很短的段落变得模糊或分裂,在去神经6个月的肌肉,有些慢纤维仅局部结构模糊但绝大部分地区呈现结构完好,这说明这种鸟类的混合肌的慢纤维在去神经后结构上仍有很大的稳定性。以上观察也说明这种去神经肥大的现象除了在发生原因上值得注意以外,它在肥大的程度与持久性上和其他的实验性肌肉肥大相比也是很显著的。     

FINE STRUCTURE OF CELL SURFACE SPECIALIZATIONS IN THE MATURING DUODENAL MUCOSA OF THE CHICK

Cell surfaces in the duodenal mucosa have been studied in maturing tissue of the chick from incubation until hatching. Changes in the distribution of mitoses in this tissue give an indication of its rate of maturation. This rate is paralleled in developmental changes in microvilli and junctional complexes. Concentration of mitotic figures towards the base of villous folds is gradual from day 9 to day 16, then rapid to day 19, after which the mature pattern is acquired. By day 11, microvilli appear in a regular pattern which does not alter through hatching. Their height remains the same to day 16 when it increases gradually to day 19, then very sharply. The angle formed between the microvilli and the cell surface increases gradually to day 16, giving evidence of advancing internal structure. Changes in cell adhesion also occur at day 16. Thereafter, following trypsin treatment cells are held together in patches by the tight junctions of the terminal bar, although the desmosomes are separated. The timing of these morphological changes is compared with that of alkaline phosphatase accumulation in this tissue as reported by Moog (13). Increase in the surface area of the microvilli parallels the increase in the activity of the enzyme.     

METHYLAMINE UPTAKE IN THE GREEN ALGA CHLORELLA PYRENOIDOSA1

Methylamine uptake in nitrogen-starved Chlorella pyrenoidosa Beij. follows Michaelis-Menten kinetics: maximum uptake is about 1.6 nmol μl^?1· cells · min^?1, half-saturation occurs at 4 μM methylamine, and the slope in the range where uptake is proportional to concentration is 0.4 nmol μl^?1· min^?1·μM^?1. In cells grown in the presence of a non-limiting nitrogen concentration, methylamine uptake is directly proportional to concentration up to at least 0.5 mM, and the slope is 1/500 that for starved cells. Similar uptake kinetics have been reported for Penicillium chrysogenum and attributed to an inducible “ammonium permease.” Apparently, a similar permease occurs in algae.     

THE FINE STRUCTURE OF EMBRYONIC CHICK SKELETAL MUSCLE CELLS DIFFERENTIATED IN VITRO

Dissociated myoblasts from 12-day chick embryos were cultured in monolayer, and the differentiation of skeletal muscle cells was studied by electron microscopy. The results have revealed a striking ultrastructural similarity between the in vivo and the in vitro developing muscle, particularly with respect to the myofibrils and sarcoplasmic reticulum. This study demonstrates that all the characteristic organelles of mature skeletal muscle can develop in vitro in the absence of nerves.     

ENDOGENOUS LEVELS OF INDOLE-3-ACETIC ACID IN SYNCHRONOUS CULTURES OF CHLORELLA PYRENOIDOSA12

Endogenous levels of indole-3-acetic acid were mesaured in synchronous cultures of Chlorella pyrenoidosa (TX-7-11-05). The cultures were synchronized by alternating light:dark periods of 15:9 hr at a temperature of 40 ± 1 C. After 2 synchronous cycles the cultures were exposed to a low light treatment of 350 ± 100 ft-c. The time to incipient cell division under these conditions was 6 hr and 15 min. Samples were taken at 3 sampling periods during the low light treatment period:low light 0 hr (LL0); low light 3 hr (LL3); and low light 6:15 hr (LL6:15). The algal extracts were analyzed by a fluorometric procedure which measured the indole-α-pyrone product formed by the action of the trifluoracetic acid-acetic anhydride reagent with IAA. The IAA levels increased gradually from the autospore stage (5.19 μg × 10^?4/mg dry wt) to the adolescent stage (7.13 μg × 10^?4/mg dry wt) and more rapidly when approaching the ripened adult stage (14.55 μg × 10^?4/mg dry wt). The mean percentage increase from autospore to adolescent was 36.9%, and from adolescent to ripened adult 104.6%. The total percentage increase from autospore to adult was 180.3%. Levels of IAA were 2 times higher just prior to division than in the autospore stage.