Francis D, Barlow P W
School of Pure and Applied Biology, University of Wales, Cardiff, UK.
Symp Soc Exp Biol. 1988;42:181-201.
During the period between successive divisions, a cell traverses three stages of interphase: G1 (pre-synthetic interphase), S-phase (DNA synthetic interphase) and G2 (post-synthetic interphase). The time taken for all cells in a meristem to divide (the cell doubling time (cdt] decreases in response to an increase in temperature. For example, the cdt in root meristems of Zea mays decreases 21-fold as the temperature is increased from 3 to 25 degrees C. Whether all phases of the cell cycle alter proportionately with temperature has been ascertained by comparing data from the root meristem of five species: Pisum sativum, Helianthus annuus, Tradescantia paludosa, Allium cepa and Triticum aestivum. In three of the five species there is a disproportionate lengthening of the G1 phase at low temperatures. We suggest that arrest in G1 with the associated 2C amount of DNA, confers maximal protection on the genome of a somatic cell to the stress of low temperature. DNA replication has been studied at different temperatures for Helianthus annuus, Secale cereal and Oryza sativa. The rate of DNA replication, per single replication fork, increases when the temperature is raised, while the distance between initiation points (replicon size) remains constant. The temperature at which the cell cycle has a minimum duration is close to 30 degrees C in many species, and it seems that this optimum temperature is always near the upper temperature limit of the cell cycle. The rate of cell division determines the rates of organ and cell growth. Thus, temperature has a major effect on the way in which meristematic cells are deployed in organogenesis. The rate of organogenesis, in turn, determines the response of the plant to the growing season. We predict that species growing in sub-arctic conditions comprise cells with low DNA contents and hence have the potentialities for rapid cell cycles so that maximum advantage can be taken of a short growing season. Data from Triticum aestivum show that at 5 degrees C, nucleoli are large compared with those at 10-25 degrees C. These observations are consistent with high levels of RNA polymerase and cellular RNA found at low compared with high temperatures. These responses may be important in sustaining growth at 5 degrees C. Finally, the effects of temperature on developmental transitions are discussed. The picture that emerges is that more is known about low, as opposed to high, temperature as a morphogenetic switch but virtually nothing is known about cell cycle activity during such transitions.(ABSTRACT TRUNCATED AT 400 WORDS)
在连续两次分裂之间的时期，细胞经历分裂间期的三个阶段：G1期（合成前期）、S期（DNA合成期）和G2期（合成后期）。分生组织中所有细胞分裂所需的时间（细胞倍增时间，cdt）会随着温度升高而减少。例如，玉米根分生组织中的cdt在温度从3摄氏度升高到25摄氏度时下降21倍。通过比较豌豆、向日葵、紫露草、洋葱和小麦这五个物种根分生组织的数据，已确定细胞周期的所有阶段是否都与温度成比例变化。在这五个物种中的三个物种中，低温下G1期会不成比例地延长。我们认为，处于G1期且伴有2C含量的DNA，能为体细胞基因组提供对低温胁迫的最大保护。已在不同温度下对向日葵、黑麦和水稻的DNA复制进行了研究。每个复制叉的DNA复制速率在温度升高时会增加，而起始点之间的距离（复制子大小）保持不变。许多物种中细胞周期持续时间最短的温度接近30摄氏度，而且这个最适温度似乎总是接近细胞周期的温度上限。细胞分裂速率决定了器官和细胞的生长速率。因此，温度对分生组织细胞在器官发生过程中的分布方式有重大影响。反过来，器官发生速率决定了植物对生长季节的响应。我们预测，生长在亚北极条件下的物种含有低DNA含量的细胞，因此具有快速细胞周期的潜力，以便能充分利用短暂的生长季节。小麦的数据表明，在5摄氏度时，核仁比在10至25摄氏度时大。这些观察结果与低温下与高温相比发现的高水平RNA聚合酶和细胞RNA一致。这些反应可能对在5摄氏度时维持生长很重要。最后，讨论了温度对发育转变的影响。出现的情况是，作为形态发生开关，人们对低温而非高温了解更多，但对于此类转变期间的细胞周期活动几乎一无所知。（摘要截选至400字）
