Fruits of the actinidia genus.

Kiwifruit is the most well-known crop in the genus Actinidia. Although Actinidia fruit sales in the international market are dominated by a single kiwifruit cultivar Actinidia deliciosa "Hayward," there are a considerable number of cultivars and selections in the genus that have widely diverse shape, size, and hairiness. They also offer a wide variation in sensory attributes such as flesh color, flavor, and taste, and in nutritional attributes such as the vitamin C level and carotenoid content. The level of actinidin, which is a cysteine protease in kiwifruit, also varies greatly among cultivars. This chapter reviews available information related to several important components, allergenic properties, and health benefits of Actinidia fruits.

Genotypic differences in chlorophyll, lutein, and beta-carotene contents in the fruits of actinidia species.

Chlorophyll, lutein, and beta-carotene contents in Actinidia fruits were determined by high-performance liquid chromatography in various genotypes, including five Actinidia deliciosa, seven Actinidia chinensis, two Actinidia rufa, five Actinidia arguta, and three interspecific hybrids. The concentrations of chlorophyll, lutein, and beta-carotene in the fruit of A. deliciosa Hayward were 1.65, 0.418, and 0.088 mg/100 g fresh weight, respectively. Of A. deliciosa cultivars, Koryoku showed significantly higher concentrations in chlorophyll, lutein, and beta-carotene than Hayward. In most cultivars of A. chinensis, although both chlorophyll and lutein contents were significantly lower than in Hayward, the beta-carotene content tended to be slightly higher. In A. rufa, A. arguta, and their interspecific hybrids, the contents of chlorophyll, lutein, and beta-carotene were much higher than in Hayward. In particular, these fruits were found to be the richest dietary source of lutein among commonly consumed fruits.

Varietal difference in vitamin C content in the fruit of kiwifruit and other actinidia species.

Vitamin C content in the fruit of various cultivars of kiwifruit and other Actinidia species was estimated by determination of L-ascorbic acid and L-dehydroascorbic acid using ion-pair reversed-phase high-performance liquid chromatography. Fruit of A. deliciosa cv. Hayward, the most common commercially available cultivar, contained 65.5 mg/100 g fresh weight (FW) vitamin C. Vitamin C content in A. deliciosa fruit varied from 29 mg/100 g FW to 80 mg/100 g FW. In most cultivars of A. chinensis, vitamin C content in fruit was higher than that of Hayward. In particular, vitamin C content in cv. Sanuki Gold fruit reached more than 3-fold that of Hayward on a weight for weight basis. In A. argutafruit, there was wide variation in vitamin C content, with concentrations ranging from 37 to 185 mg/100 g FW. In cv. Gassan, Issai, and Mitsuko, vitamin C content of the fruit was much higher than that of Hayward. In A. arguta fruit, the ratio of L-ascorbic acid to total ascorbic acid tended to be higher than that of other species.

Purification of Co-ARIS, a Cofactor for Acrosome Reaction-Inducing Substance, from the Egg Jelly of Starfish.

In the starfish, Asterias amurensis, the acrosome reaction-inducing capacity of the egg jelly has been attributed to two components in the egg jelly: a sulfated glycoprotein (ARIS) and an unidentified low-molecular weight substance (Co-ARIS). In the process of purification of Co-ARIS, we found that Co-ARIS is not a single chemical entity but a series of closely related molecules. Co-ARIS was first group-separated by using octadecylsilane and anion-exchanger. Three major Co-ARIS' (I, II and III) were then purified by successive chromatographies using octadecylsilane and silica gel to the homogeneity in thin layer chromatography. Each of purified Co-ARIS', together with ARIS or the Pronase-digest of ARIS, induced the acrosome reaction at high ratios in normal seawater.

Correlation Between the Molecular Structure and the Biological Activity of Co-ARIS, a Cofactor for Acrosome Reaction-Inducing Substance.

Two components in the egg jelly are required for inducing the acrosome reaction in starfish; a sulfated glycoprotein called acrosome reaction-inducing substance (ARIS) and its cofactor called Co-ARIS. Three distinct molecules were isolated as the major Co-ARIS' and designated as Co-ARIS' I, II and III. Structural analysis of Co-ARIS' revealed that they are steroidal saponins comprising a sulfated steroid and a pentasaccharide chain. Co-ARIS' I and II differ only in the steroidal side chain. In the presence of ARIS, each Co-ARIS induced the acrosome reaction with a maximal effect at 100-200 µM (Co-ARIS I) or 25-50 µM (Co-ARIS' II and III). Mixtures of Co-ARIS' I, II and III were more effective than the individuals. The activity of Co-ARIS was considerably reduced by solvolytic desulfation but was not affected at all by periodate oxidation. Reduction by NaBH4 decreased the activity of Co-ARIS I and enhanced that of Co-ARIS II. Treatment of Co-ARIS III with NaBH4 did not affect the activity as anticipated from its structure. These results suggest that the sulfate moiety and the side chain of steroid are important for the activity of Co-ARIS. The saccharide chain, however, seems not necessarily to be strictly specified for the activity.

Maitotoxin, A Presumed Calcium Channel Activator, Induces the Acrosome Reaction in Mussel Spermatozoa: (maitotoxin/acrosome reaction/calcium channel activator/calcium channel antagonist/mussel sperm).

Maitotoxin, a presumed activator of the voltage-sensitive calcium channel, induced the acrosome reaction in the mussel, Mytilus edulis at physiological pH and in the starfish, Asterias amurensis at pH 9.5. The induction of acrosome reaction by maitotoxin depended upon external Ca2+ and was inhibited by two types of calcium channel blockers; verapamil and diltiazem. These results suggest that the activation of the voltage-sensitive calcium channel takes an important part in the initiation of acrosome reaction in Mytilus and other animals.

Intracellular pH Changes of Starfish Sperm Upon the Acrosome Reaction: (acrosome reaction/intracellular pH/starfish sperm/egg jelly/9-aminoacridine).

The acrosome reaction is accompanied by ionic changes such as increases in intracellular Ca2+ and intracellular pH (pHi ). Since the two jelly components essential for inducing the acrosome reaction, ARIS and Co-ARIS, were shown to activate Ca-channels (accompanying paper), we examined the jelly components to determine which was responsible for the pHi -increase using 9-aminoacridine as a probe of pHi . This paper presents evidence that an oligopeptide(s) is responsible for the pHi -increase. The pHi of swimming sperm is 7.4-7.5. Within 20 sec after the addition of jelly, their pHi increased rapidly by 0.06 pH unit, then decreased by 0.2-0.3 pH unit, and reached a plateau level within 3 min. Similar changes in pHi were observed on addition of a Pronase digest of ARIS (P-ARIS) and a diffusible fraction of jelly (Fraction M8 ) together. Fraction M8 , but not ARIS or Co-ARIS increased the pHi , and activated sperm respiration in sea water at pH 6.5. The two activities of Fraction M8 depended upon Na+ but not Ca2+ , and were susceptible to Pronase digestion. Fraction M8 is also known to enhance induction of the acrosome reaction by the Ca-ionophore A23187. These results suggest that the egg jelly contains a peptide(s) that is not obligatory for the acrosome reaction but facilitates the reaction by increasing the pHi of the sperm. The significance of the pHi -increase upon the acrosome reaction is discussed.

Acrosome Reaction-Inducing Substance Purified from the Egg Jelly Inhibits the Jelly-Induced Acrosome Reaction in Starfish: An Apparent Contradiction: (acrosome reaction/starfish sperm/egg jelly/ARIS/Co-ARIS).

Previous studies indicated that two components of the egg jelly are required for induction of the acrosome reaction in starfish: a sulfated glycoprotein called acrosome reaction-inducing substance (ARIS) and a diffusible organic substance(s) called Co-ARIS. In the present study the sites of action of ARIS and Co-ARIS and their temporal relationships were examined. When sperm had been treated for a few minutes with ARIS, or a crude preparation of Co-ARIS (Fraction M8 ), or inadequate amounts of jelly, or sufficient jelly in low Ca2+ sea water, they did not undergo the acrosome reaction when the deficiencies were corrected. Moreover, they became nonresponsive to the jelly. Pronase digest of ARIS (P-ARIS) but not of Fraction M8 retained this capacity. A steroidal saponin purified as Co-ARIS did not have this capacity. This suggests the presence of a third jelly component, probably an oligopeptide(s), participating in induction of the acrosome reaction. Activation of Ca2+ -uptake seems to be at least one, if not the only, action site of ARIS and Co-ARIS, because ARIS, P-ARIS, and Fraction M8 inhibited jelly-induced Ca2+ -uptake by sperm, and because the calcium ionophore A23187 by-passed the blockage by these components of the jelly-induced acrosome reaction.

Induction of the Acrosome Reaction in Starfish: (acrosome reaction/starfish sperm/egg jelly/Ca-channel/ionophore).

In the starfish, Asterias amurensis, at least two distinct components of the egg jelly are required for inducing the acrosome reaction: a sulfated glycoprotein named acrosome reaction-inducing substance (ARIS) and a diffusible organic substance(s) named Co-ARIS. The following evidence suggested that ARIS and Co-ARIS cooperatively activate CA-channels of the sperm plasma membrane and eventually induce dramatic changes in sperm morphology, the acrosome reaction. 1) Pronase digest of ARIS (P-ARIS) and Co-ARIS, either as a pure or a crude preparation (Fraction M8 ), were fully effective in combination for induction of the acrosome reaction in normal sea water, although they were not effective individually. P- ARIS alone induced the acrosome reaction fully in high Ca2+ sea water and markedly at high pHs, whereas Fraction M8 alone did not induce the reaction even in these conditions. The reaction was not induced by increase in either the Ca2+ concentration or the pH of sea water, but was markedly induced in the absence of jelly components by raising both the pH and Ca2+ concentration together. 2) The ionophore A23187 induced the acrosome reaction appreciably when present alone and fully in the presence of monensin or Fraction M8 . Monesin alone was ineffective. 3) The jelly or a combination of ARIS and Fraction M8 caused abrupt Ca2+ -uptake by the sperm. The Ca-channel blockers verapamil and diltiazem inhibited the jelly-induced acrosome reaction.

Anion Channel Blockers Inhibit the Acrosome Reaction of Echinoderm Sperm: (anion channel blocker/acrosome reaction/acid release/stafish/sea urchin).

Two types of anion channel blockers, SITS (4-acetamide-4'-isothiocyanostilbene-2,2'-disulfonic acid) and DIDS (4,4'-diisothiocyanostilbene-2, 2'-disulfonic acid), inhibited jelly-induced acrosorne reaction in starfish and sea urchin. In starfish sperm, both of the blockers reversibly inhibited the formation of acrosomal process but they had no effect on either the acrosomal exocytosis or acid release from the sperm. Complete acrosome reaction occurred even in Cl- - and SO4 2- -free artificial seawater whereas HCO3 - was required for the acrosomal exocytosis. Importance of anion transport in acrosome reaction is discussed.