
Many abiotic variables affect plants, e.g. levels of light, carbon dioxide and water. One of the most important of those non-biotic factors is temperature. Now, given its importance you could be forgiven for assuming that it is recorded accurately and correctly. Unfortunately, that isnβt always the case. Take for instance the temperature of the meristem (symbolised as Tmeristem), which is important in driving plant development. For such a crucial aspect of plant biology studies have largely relied on measuring the temperature of the air surrounding the plant (Tair). Tair is measured because it is assumed to represent the meristem temperature because plants are poikilotherms (organisms whose βinternal temperature varies considerably β¦ Usually the variation is a consequence of variation in the ambient environmental temperatureβ). Whilst that assumption may seem reasonable β and it does save the would-be investigator the trouble of penetrating the umpteen layers of developing leaves, etc, that may sheathe the apical meristem, it is nonetheless an assumption. And the veracity of assumptions must be tested, which is what Andreas Savvides et al. did. Guess what they found! Thatβs right: Tmeristem differed from Tair β ranging between β2.6 and 3.8 Β°C in tomato, and β4.1 and 3.0 Β°C in cucumber(!). As the team conclude, βfor properly linking growth and development of plants to temperatureβ¦ Tmeristem should be used instead of Tairβ.
If youβre now intrigued by detecting temperatures within cells, you might like to explore the nanoscale thermometer developed by G. Kucsko et al. Using βquantum manipulation of nitrogen vacancy (NV) colour centres in diamond nanocrystalsβ it can detect temperature variations as small as 44 mK(!) and can measure the local thermal environment at length scales as low as 200 nm(!!). Or, if you want a more biological approach, check out the genetically encoded sensor that fuses green fluorescent protein to a thermosensing protein derived from Salmonella, as showcased by Shigeki Kiyonaka et al. Although proof of this particular principle was demonstrated with thermogenesis in the iconic mitochondria of brown adipocytes (and the somewhat less iconic endoplasmic reticulum of myotubes), the team envisage it could be used to investigate this phenomenon in other living cells. Maybe even within the cone cells of tropical cycads that undergo impressive increases in temperature, where Tcone can be markedly greater that Tair. In view of concerns about global temperature changes and effects of temperature on regulation of such economically important processes as flowering, accurate temperature information in planta β and an appreciation of the temperature that plants are actually responding to β is likely to become increasingly important.
[For a useful set of slides summarising Savvides et al.βs work, visit slideshare.net. For a less physics-oriented interpretation of the Nature nanoscale thermometry article try the accompanying βNews and Viewsβ item by Konstantin Sokolov β Ed.].
Interesting. Now we need to see if their are constant relationships between the two t’s across species.