DEVELOPMENT OF THE STIGMATIC SURFACE OF PRUNUS AVIUM L., SWEET CHERRY

The stigmatic papillae of sweet cherry were examined to determine developmental characteristics of the wet-stigma surface. Early stages of secretion are detectable 1 wk prior to anthesis by using a 1% crystal violet solution. The number of stainable cells and the amount of interstitial staining subsequently increase, although secretions are not visible on unstained specimens until anthesis. Auto-fluorescence above 500 nm (excited by 335–480 nm) becomes microscopically detectable at floral maturity and grows more intense after anther dehiscence. Light microscopy of plastic sections shows that papillae degenerate in peripheral regions of unpollinated mature stigmas, and that this is even more pronounced in pollinated ones. The distal portions of the papillae are covered with a homogeneous cuticular cap, which when viewed with electron microscopy encloses a subcutaneous secretion prior to cuticle exfoliation. Other exudates observed with electron microscopy prior to anthesis are interstitial electron-translucent globules and surrounding matrix, and assorted vesicles, lipid globules, and starch grains which are present at floral maturity. Flowers observed under field conditions in the terminal secretion stage accumulate trichomatous structures. Our observations indicate that the stigma of Prunus avium L. is characterized by several phases of secretion which appear to be facilitated by mechanical abrasion. A model for the primary pollen-receptive area is proposed and suggestions are made concerning the origin of the secretions.     

FACTORS AFFECTING THE SECRETION OF LUTEINIZING HORMONE IN THE EWE

(1) Luteinizing hormone (LH) is secreted as discrete pulses throughout all stages of the reproductive cycle of the ewe, including pre-pubertal, seasonal and lactational anoestrus, and the luteal and follicular phases of the oestrous cycle. Secretion is probably also pulsatile during the preovulatory surge of LH. (2) The secretion of LH is affected by the ovarian steroids, oestradiol and progesterone, both of which act principally to reduce the frequency of the pulses. During the luteal phase the two steroids act synergistically to exert this effect, and during anoestrus oestradiol acts independently of progesterone. Androstenedione secreted by the ovary apparently has no role in the control of LH secretion. (3) The amplitude of the pulses may also be affected by the steroids but there are conflicting reports on these effects, some showing that amplitude is lowered by the presence of oestrogen and others showing increases in amplitude in the presence of oestrogen and progesterone. (4) The secretion of LH pulses is affected by photoperiod, social environment and nutrition. Under the influence of decreasing day-length, oestradiol alone cannot reduce the frequency of pulses and the ewe experiences oestrous cycles. When day-length is increasing, the hypothalamus becomes more responsive to oestradiol which reduces the frequency of the pulses. (5) A hypothetical pheromone secreted by rams can increase the frequency of the LH pulses in anoestrous ewes and thereby induce ovulation, possibly by inhibiting the negative feedback exerted by oestradiol. (6) The relationships between nutrition and reproduction are poorly understood, but it seems likely that the effects of nutrition are mediated partly through the hypothalamus and its control of the secretion of LH pulses. (7) The pulses of LH secreted by the anterior pituitary gland are evoked by pulses of GnRH secreted by the hypothalamus. The location of the centre controlling the GnRH pulses and the neurotransmitter involved are not known.     

AN ECOPHYSIOLOGICAL STUDY OF THE SALT SECRETION OF FOUR HALOPHYTES

Plants of Spartina anglica, Limonium vulgare, Armeria maritima and Glaux maritima were collected in the field and grown on different concentrations of NaCl, KCl and CaCl₂. Salt secretion, ion content, water content and transpiration rates were determined. The highest sodium secretion was found in Spartina anglica , a species from the most saline habitat; and a somewhat lower secretion rate in Limonium vulgare. The lowest rates were found in Glaux maritima and Armeria maritima. The sodium secretion efficiency, i.e. the ability to maintain an unchanged internal sodium content, was highest in Spartina anglica. Spartina anglica is the most successful in the removal of excessively absorbed salt, since it secretes 60% of the absorbed sodium. The values for Limonium vulgare, Glaux maritima and Armeria maritima were 33, 20 and 4% respectively. The species studied differ in the preferential sequence of ion secretion as well as in secretion rate and efficiency. This preferential sequence of ion secretion seems to be similar in members of the same taxonomic group (Plumbaginaceae). The comparability of the secretion parameters is discussed with regard to morphological differences between the species.     

ON THE MECHANISM OF MILK SECRETION : THE INFLUENCE OF INSULIN AND PHLORIDZIN

The four types of experiments on milk secretion herein described really fall into one general class so far as the physiological effects produced are concerned. Starvation lowers the blood sugar and raises the osmotic pressure of the blood. The experiment using parathyroid hormone with or without starvation may have its effects interpreted as simply due to starvation since 1000 units of this hormone produced no visible effects on the blood calcium or milk constituents different from those of starvation. Since insulin produces a marked and rapid drop in blood sugar it too may be looked upon as a rapid starvation effect. It has some other important effects, however. Briggs et al. (21) have shown that potassium and phosphorus of the blood are decreased and Luck, Morrison, and Wilbur (22) indicate a reduction in the amino acids of the blood in insulin treatment. Phloridzin lowers the threshold for sugar retention with the consequence that in time it tends to lower the sugar of the blood to an even greater extent than that noted in starvation. It tends to depress the potassium, to increase the phosphorus content of the blood, and to cause the body to burn protein rather than carbohydrate, thus increasing nitrogen excretion. All of the experiments are characterized by a sharp reduction in the milk yield. Cary and Meigs (23) have studied like reductions in milk yield produced by varying the energy or protein of the diet. They conclude that such decrease in milk production may be interpreted as due to the direct effect of the starvation and the consequent reduction of the energy and protein available to milk secretion. The reduction in milk yield for the experiments herein described can undoubtedly be attributed to the same causes as those cited by Cary and Meigs. The experiment where Cow 47 was given a full ration and at the same time injected with large quantities of insulin is of particular interest in this connection. The ration was adequate and the cow ate well, yet her production declined to a fifth of her normal milk yield. Her chart shows that there was a slight reduction in her blood sugar when insulin was introduced into the blood stream. It seems furthermore likely that this sugar was not as available to milk secretion, since there appears to be more than a corresponding drop in the lactose content of the milk. The work of Luck et al. would seem to indicate that there should be a like drop in the amino acids of the blood. These two conditions would lead, according to the work of Cary and Meigs, to a reduction in the concentration of the nitrogen of the milk. Actually, in the experiment as it was performed, the nitrogen increased to a value about 40 per cent above normal. A somewhat similar conflict is noted in two of the other three insulin experiments where starvation accompanied insulin injection. To this extent it would seem that the factor deserving most emphasis in its immediate effect on milk yield is the energy available, and that the later and more secondary factor is the amino acid concentration of the blood. In the starvation experiments, the butter fat percentage of the milk rises rather uniformly with the duration of starvation. In the insulin experiments, however, the charts appear to show a marked reduction in this butter fat percentage immediately after the introduction of insulin. This is particularly noticed after the second and third injections. Since the dextrose of the blood tends to be reduced and made unavailable to the general physiological processes by the presence of the large excess of insulin, and since this reduction of the butter fat percentage is noted as an accompanying phenomenon, it would appear that the blood dextrose plays a part in the synthesis of milk fat as well as being the source of the milk lactose, possibly as a source of energy in converting body fat to butter fat. In this regard the results for the treatment of Cow 47 with phloridzin are of importance. As noted by others, the introduction of phloridzin causes a marked rise in the fat percentage of the milk. The lactose per cent is also higher than that noted in starvation. Since phloridzin, by lowering the threshold for the blood sugar, causes large quantities of it to be drained from the body through the urine, and therefore reduces the reserve supply, it follows that if the insulin hypotheses are correct we should expect an eventual lowering of the lactose and of the fat below the starvation level. During the last of the experiment this is what was actually observed. The effects of starvation and of insulin furnish concordant proof for the theory that the lactose of milk is derived from the sugar of the blood. The fact that the different constituents of the milk, the fat, the lactose, the nitrogen, and the ash, do not exactly parallel each other in their behavior throughout these experiments indicates that they have in all probability separate origin. This is particularly true of the butter fat percentage, which appears to have a rate of secretion which is more or less independent of the other constituents, and higher in amount. This result would fall in line with the conclusion of the writers in a previous paper in which it was indicated that the fat of the blood was very likely deposited in the udder as fat corresponding to body fat from which source it was metabolized into the fat of milk shortly before it was needed for milk secretion. The wide variation brought about in the constituents of the milk by the treatment all point to the conclusion that in milk secretion a balance is maintained between the osmotic pressure of the milk and of the blood. Thus when the sugar of the milk is reduced either through starvation or by insulin the ash constituents rise to compensate for this reduction and make the osmotic pressure of the milk similar to that of the blood. These results further appear to indicate that the salts and the sugars are more or less independent in their passage and metabolism into milk from the other constituents. These observations are therefore in line with those obtained by Jackson and Rothera (14) and by Davidson (15) in their brilliant experiments where they modified milk secretion by returning milk or milk sugars and salts to the udder. These experiments give direct proof for the conclusion that modifications of the blood of dairy cattle produce direct and predictable modification of the milk secreted.     

STRUCTURAL DIMORPHISM OF STIGMATIC PAPILLAE IN DISTYLOUS LINUM SPECIES

Intermorph differences in the wall structure and constituents of stigmatic papillae are described for distylous Linum pubescens and L. grandiflorum. In the long-styled morph of both species the wall portion around the apex of the papilla has a thickened cellulose-pectin layer. In the short-styled morph of L. pubescens a cap zone is interposed between the cuticle and apical portion of the papilla wall. The subcuticular cap space contains pectins and lipid particles. Similar particles are also present in deposits on the cuticle surface. Papillae of the short-styled morph in L. grandiflorum lack a cap zone and have only epicuticular lipid deposits. Other distylous Linum species in which the two morphs differ in wall structure of the papillae are L. mucronatum, L. flavum, L. perenne, L. austriacum, and L. maritimum. Studies of stigma dimorphism can help to elucidate evolutionary relations between dimorphic and monomorphic Linum species.     

SOME ASPECTS OF SECRETION : I. SECRETION OF WATER

If we increase the osmotic pressure at one end of a Nitella cell by applying a solution of sucrose and if we subsequently submerge the entire cell in water we find that water enters at the end where the osmotic pressure is higher and comes out of the cell at the other end. If similar inequalities of osmotic pressure should arise as the result of metabolism we can understand how a secreting cell might take up water at one spot on its surface and expel it in another spot and thus bring about the secretion of water. The Nitella cell can expel water from a region of the cell which is in contact with water, air, or mineral oil.     

垂体前叶内神经纤维可能参与ACTH分泌的调节

我们建立了垂体组织块短时温育并施加电场刺激的离体实验体系,运用此方法并结合放射免疫测定激素含量,观察了大鼠垂体前叶内神经纤维对促肾上腺皮质激素（ＡＣＴＨ）释放的影响。结果表明,电场刺激能够促使垂体前叶ＡＣＴＨ释放显著增加,刺激参数为强度３０ｍＡ,波宽０．５ｍｓ,频率１０Ｈｚ。这个效应可为温育液中加入河豚毒素（ＴＴＸ）和藜芦碱所阻断,但ＴＴＸ不能阻断精氨酸加压素（ＡＶＰ）诱发的ＡＣＴＨ分泌。同样参数的电场刺激对分散培养的大鼠垂体前叶细胞ＡＣＴＨ的分泌没有显著作用。以上结果说明,我们所用参数的电场刺激产生的效应是兴奋了垂体前叶内的神经纤维,而非直接刺激腺细胞所致。上述结果提示：垂体前叶激素分泌的调节除了传统的体液途径之外,还可能存在直接的神经控制。     

溶酶体在垂体—肾上腺皮质激素分泌调节中的作用

本实验用地塞米松造成大鼠垂体促皮质激素细胞及其靶腺肾上腺皮质束状带细胞分泌抑制,对这两种细胞中的溶酶体及分泌自噬和自体吞噬活动进行了超微结构观察、CMP 酶细胞化学定性和形态计量。实验结果显示,在分泌受抑制状态下,垂体促皮质激素细胞中分泌自噬和自体吞噬作用加强,与此同时,肾上腺皮质细胞中自体吞噬作用也业著加强。这些结果表明,在分泌类固醇激素的细胞中,溶酶体以自体吞噬的方式清除一部分生产激素的细胞器,可能是一种普遍存在的分泌调节机制,正如在分泌蛋白质和肽类激素的细胞中普遍存在着分泌自噬这一调节机制一样。     

内分泌细胞中溶酶体对激素分泌调节的作用

本实验用外源性雄激素引起垂体促性腺激素细胞和睾丸间质细胞分泌抑制,对这两种细胞中的溶酶体及分泌吞噬和自体吞噬活动进行了超微结构形态观察和半定量分析。实验中应用了CMP酶细胞化学技术和免疫胶体金技术。研究结果显示,在分泌受抑制状态下,垂体促性腺激素细胞中溶酶体增多,分泌吞噬活动加强;与此同时,睾丸间质细胞也表现溶酶体增多、自体吞噬活动加强。这些结果不仅再次证明在分泌蛋白质激素细胞中溶酶体以分泌吞噬的方式参与了激素分泌调节,更重要的是初步证明在分泌类固醇激素细胞的分泌调节中,也有溶酶体的参与,其形式是自体吞噬作用。细胞通过自体吞噬作用得以在短时间内清除一部分合成激素的细胞器和其中的激素,这可能是分泌类固醇激素的细胞及时有效地调整激素分泌量的一项重要机制,与分泌蛋白质激素细胞的分泌吞噬有着相同的意义。     

褶纹冠蚌外套膜组织培养的分泌物的偏光显微镜观察

以淡水育珠贝中珍珠形成较快的褶纹冠蚌为材料,用相差显微镜观察组织培养的外套膜的分泌物的形成和变化,用偏光显微镜观察分泌物的双折射现象,并与活体外套膜的分泌物、贝壳的角质层、棱柱层、珍珠层的双折射现象进行比较。结果表明;离体培养的外套膜细胞不仅能产生活体细胞相同的分泌物,而且分泌物还能在培养过程中形成结晶,并逐渐生长。发现外套膜的不同部位分区培养所形成的分泌物的性状与结晶性质和活体有一致性,表明组织培养的外套膜小片具有贝体原来的组织结构、分化特征和分泌功能。     

IN VITRO STIMULATION OF ENZYME SECRETION AND THE SYNTHESIS OF MICROSOMAL MEMBRANES IN THE PANCREAS OF THE GUINEA PIG

Several mechanisms have been suggested to explain how secretory cells remove from the plasmalemma the excess membrane resulting from the insertion of granule membrane during exocytosis: intact patches of membrane may be internalized and then reutilized within the cell; alternatively these membranes may be either disassembled to subunits or degraded. In the latter case new membranes should be synthetized at other sites of the cell, probably in the rough-surfaced endoplasmic reticulum (RER) and the Golgi complex. In the present research, membrane subfractions were obtained from rough microsomes (derived from fragmented and resealed RER cisternae) and from smooth microsomes (primarily contributed by Golgi stacks and vesicles) of the guinea pig pancreas by incubation at 4°C for 4 hr in 0.0005 M puromycin at high ionic strength followed by mild (pH 7.8) alkaline extraction with 0.2 M NaHCO₃. Such treatments release the majority of nonmembrane components of both microsomal fractions (i.e., contained secretory enzymes, ribosomes, and absorbed proteins of the cell sap) and allow the membranes to be recovered by centrifugation. The effect of in vitro stimulation of enzyme secretion (brought about in pancreas slices by 0.0001 M carbamoyl choline) on the rate of synthesis of the phospholipid (PLP) and protein of these membranes was then investigated. In agreement with previous data, we observed that in stimulated slices the synthesis of microsomal PLP was greatly increased. In contrast, the synthesis of microsomal membrane proteins was unchanged. These results suggest that exocytosis is not coupled with an increased rate of synthesis of complete ER and Golgi membranes and are, therefore, consistent with the view that excess plasma membrane is preserved and reutilized, either as discrete membrane patches or as membrane macromolecules, throughout the secretory cycle.