REVERSION AND REINDUCTION OF FLOWERING IN PERILLA

Lam , S. L., and A. C. Leopold . (Purdue U., Lafayette, Indiana.) Reversion and reinduction of flowering in Perilla. Amer. Jour. Bot. 48(4): 306–310. Illus. 1961.—Plants of Perilla crispa (Thunb.) Tanaka ultimately revert to the vegetative state provided that they have received not more than about 20 cycles of short photoperiods. Reversion is markedly promoted by repeated debudding of plants induced with 35 cycles or less. Reverted plants of Perilla could be reinduced twice by photoperiodic treatment of the originally induced leaves. Timing experiments to measure the flow of flower stimulus from induced leaves suggest a gradual loss of the stimulus, as indicated by increased time to appearance of flowers and decreased flower number. It is concluded that after the inductive treatment is withdrawn, the effectiveness of the flower stimulus coming from the leaf declines with time. It is suggested that reversion is made possible by the decline of effective flower stimulus coming from the induced leaves.     

THE QUANTITATIVE ULTRASTRUCTURE OF THE MERISTEMATIC CELLS OF XANTHIUM STRUMARIUM DURING THE TRANSITION TO FLOWERING

Ultrastructural changes occurring in the central part of the apical meristem of the SDP Xanthium strumarium, induced to flower by a single 16-hr long night, were quantitatively investigated using stereological methods and compared to the changes previously reported in other species, particularly the LDP Sinapis alba. Changes detected in Xanthium, which are also found in other species, included: increase in cellular, cytoplasmic, cytoplasmic matrix and nucleolar sizes, change in nucleolar structure; increase in mitochondrial number and chondriome size, increase in dictyosome number. These changes are believed to be essential for floral evocation because of their universality. Other changes were specific to Xanthium and not detected in Sinapis. Accordingly, they were thought to be accompanying nonessential events of floral evocation in Xanthium. These changes included an increase in the number of plastid profiles and in plastidome size. The size of the nucleus, chromatin and vacuolar apparatus, as well as the number of vacuolar profiles, did not change in Xanthium, contrary to what was observed in other plants.     

PHOTOPERIOD EVIDENCE IN THE INTRODUCTION OF XANTHIUM STRUMARIUM TO TAHITI AND HAWAII FROM MEXICO

Successful invasion of islands in the Pacific by Xanthium probably resulted from the chance introduction of a morpho-physiological form adapted to subtropical coastal habitats in North America. This hypothesis was tested by comparing naturalized plants from Tahiti in the Society Islands and Oahu in the Hawaiian Islands with collections from various coastal sites in Mexico. Plants from Tampico and Ciudad Mante, Tamaulipas; Veracruz (Antigua), Veracruz; and Salina Cruz, Oaxaca have morphological and physiological similarity to the Pacific introductions; however, each collection has certain niche relations that are slightly different from each other. All of the collections are in the same morphological complex and have apparent critical nights of 10.75–11 hr for reproduction. This morpho-physiological form is probably indigenous to Mexico, and it is widely distributed on the northeastern coastal plain of Tamaulipas.     

PHOTOPERIODIC ADAPTATION TO LATITUDE IN XANTHIUM STRUMARIUM

Photoperiodic responses of collections of Xanthium strumarium L., grown from seed obtained in nature at various localities in North America between latitudes 20° and 45.5° N, were examined. The critical night length was found to vary noticeably with latitude of origin, from about 7.5 hr in the northernmost strains to above 10 hr in the southern strains. These differences are considered to represent genetic adaptation of the reproductive system to environmental variables as a result of natural selection. Several strains showed a quantitative short day response rather than the more usual qualitative response. Strains from Hawaii exhibited a surprisingly tardy and erratic short-day response with a critical night length of about 11 hr, which may be an adaptation to a tropical climate.     

PHOTOPERIOD IN XANTHIUM POPULATIONS FROM TEXAS AND MEXICO

Photoperiodic responses of Xanthium strumarium L. originating between 19° N in Mexico and 34° N in Texas varied among seedlings grown from seed under controlled conditions. The critical night lengths form a gradient from 9.5 hr in northern Texas to 10.75 hr in southern Texas and northeastern Mexico. Populations with critical night lengths of 9.5 and 9.75 hr showed a longer interval to flower bud formation under cooler temperatures (24 C day/15 C night) than under warmer temperatures (30 C day/24 C night). Three of four populations with a 10.75-hr critical night length showed a shorter interval under the cooler temperature regime. Although the Texas populations demonstrate a strong correlation of photoperiodic response with latitude, the Mexico populations show diverse photoperiodic timing from approximately the same latitude. The study emphasizes that a combination of critical night length and ripeness-to-flower (maturity) response forms the basis for reproductive adaptation in different climatic regimes in Texas and Mexico.     

MOVEMENT OF THE FLOWER STIMULUS IN XANTHIUM

A distribution pattern of the flower stimulus is clearly demonstrated. The direction of the movement of the flower stimulus could be altered either by application of GA or by removal of the plant organs concerned. Dormant buds responded to the flower stimulus provided that the flower stimulus was forced down by means of decapitation and disbudding or was raised to a high level by increasing the number of the inductive cycles. A photoperiodically insensitive leaf which had been exposed to short days can still exert the inhibitory effect on flowering.     

QUANTITATIVE STUDY OF NUCLEIC ACIDS AND PROTEINS IN THE SHOOT APEX OF SINAPIS ALBA DURING TRANSITION FROM THE VEGETATIVE TO THE REPRODUCTIVE CONDITION

Quantitative changes in DNA, histone, RNA, and total protein have been measured in meristematic cells during floral evocation.² A single 22-hr, long-day exposure induced two-month-old vegetative plants of Sinapis alba to flower. Periodic collections of shoot apices were made and stained with Schiff's reagent (DNA), azur B (RNA), alkaline fast green (histone), and naphthol yellow S (total protein). The two-wavelength method was used for DNA and histone measurements and the one-wavelength, two-area procedure was chosen for RNA and total protein determinations. The DNA and histone amounts per cell decreased to a minimum value 34 hr after treatment, and most of the nuclei shifted from 4C to 2C values. DNA and histone quantities paralleled each other from 34–46 hr, after which time the histone values continued to increase and the DNA values decreased. The RNA values increased rapidly after treatment as did the total protein quantities, after a slight decrease at 34 hr concurrent with the 4C to 2C cell population shift. The significance of these events is discussed in relation to the changes which were previously described in the shoot apex of Sinapis in transition to flowering.     

华夏植物区系理论与有花植物的起源

本文评述了有花植物起源的各种理论．作者支持张宏达教授提出的华夏植物区系理论,并把该理论与北极起源说和热带起源说作了比较,要点如下：（１）北极起源说和热带起源说都从海陆不变的观点出发,而忽视了中国广大亚热带地区的丰富植物区系,因此这两个理论无法解释越来越多的新发现;（２）华夏植物区系起源说以大陆漂移理论为基础,符合中国亚热带植物区系的实际,该理论正为植物学界广泛接受;（３）有花植物起源的问题,将随着华夏植物区系理论的广泛应用以及古植物学等相关学科的发展而得到解决．     

REGULATORY ROLE OF INDOLE-3-ACETIC ACID AND GIBBERELLIC ACID IN VEGETATIVE DEVELOPMENT OF XANTHIUM PENNSYLVANICUM

A single application of gibberellic acid to young internodes significantly accelerated the rate of internode growth and the rate of leaf production in shoots of Xanthium pennsylvanicum Wallr. The average duration of one plastochron in treated plants was reduced to 43% of control levels. Gibberellic acid also had a pronounced morphogenetic effect on leaves so that the area and leaf length of treated plants were both significantly reduced. Depending upon concentration, auxin had both inhibitory and promotive effects on Xanthium shoots. Indole-3-acetic acid markedly altered the response of the gibberellic acid-treated internodes and those located above and below the site of application. In addition, high auxin concentrations induced the formation of adventitious roots in treated internodes. Auxin also brought about significant reductions in the length and area of leaves developed under the influence of this hormone.     

牡丹苗端由营养生长转向生殖生长过程中超微结构研究

电镜观察了营养生长和生殖生长两个发育埋藏的牡丹（Ｐａｅｎｉａ ｓｕｆｆｒｕｔｉｃｏｓａ．）苗端。结果如下：（１）营养生长期,原套和原体的细胞壁厚薄不均,多有胞间连丝分布。两者细胞核内均在较多异染色质。细胞质内含许多质体、嗜锇细胞主少量的线粒体,内质网和高尔基体。质体无片层结构,部分质体有淀粉粒和脂滴。原体细胞的液泡化过程比原套细胞略高。原体下方扁平细胞的大部分空间被大量的淀粉质体和液泡占据,淀粉粒