Plants in Action

Xylem elements supplying water to a transpiring leaf are normally under tension. When such a leaf is excised, xylem sap retreats towards the transpiring leaf blade to an extent that varies according to that tension. If the excised leaf is now sealed into a pressure chamber with the cut petiole protruding (Figure 1a) and pressure applied (Figure 1b), xylem sap can be forced back to the cut surface (Figure 1c). That point, or balancing pressure (BP), is taken as numerically equivalent (although opposite in sign) to the original xylem tension.

Figure 1 Operation of a pressure camber for measurement of bulk leaf xylem water potential. (a) Insertion of a detached leaf into a chamber with cut petiole protruding through a sealed aperture in the lid. In practice, this leaf would be held within a plastic bag prior to excision and during subsequent measurement to avoid moisture loss. Gas pressire is applied (b) until the cut surface of the protruding petiole moistens (c) (normally viewed with a binocular microscope for safety and as an aid to precision. Excess pressure has been applied here to emphasise sap extrusion. (Photograph courtesy E. A. Lawton)

Some physiologists believe that wat replica watches uk er content as a percentage of what could be held at saturation (relative water content, RWC) is a better index of water status than . Since the vacuole (internal sap) occupies at least 80% of the volume of the mature cell, the water content of the vacuole largely control replica watches uk s the volume of the protoplast. Hence RWC is an index of the relative volume of the symplasm. The relationship between BP and RWC is therefore known as a pressure curve. It is produced by starting with a near saturated leaf or shoot (BP 0, RWC 100) and allowing it to dry out on the laboratory bench between readings of BP in the pressure chamber. The material is weighed between readings. BP increases rapidly at rst but slows down as the wilting point is approached. Eventually, the turgor loss point (0) is reached whose P0 = 0 and = 0 = 0. Further reduction in is much slower and is linear in the absence of the turgor component. After several points have been obtained for the linear section, the material is oven dried and RWC calculated for each reading:

Instead of plotting RWC against BP, it is usually plotted a replica watches uk gainst the inverse, 1/BP, with reduction in water content proceeding from left to right (Figure 2). A straight line is tted to the lowest (below turgor) part of the curve and extrapolated to the y axis to produce the inverse of the osmotic potential at full turgor (100) (Figure 3a) where the rounded part of the curve that departs from the straight line locates the positions of 1/0 and RWC0. The real reason for inverting BP is that the line can also be extrapolated on the right to the x axis this is the RWC beyond which no amount of tension will remove the water adhering to the cell wall polysaccharides, and is called the apoplasmic or bound (B) water. Its calculation is tentative at best (because the slope is so shallow small errors could have a large effect on the value obtained).

The nal parameter calculated is the bulk elastic modulus (e). This is how much strain (reduction in relative cell volume) occurs in response to a certain stress (in this case a lowering of the water potential). It is actually an inverse measure of how elastic the bulk of the tissues are. In its simplest form, it is the slope between the two endpoints: saturation (RWC100, 100) and turgor loss point (RWC0, 0) (Figure 3a). As it is the protoplasts that actually change volume, the formula is usually corrected for apoplasmic water (B), that is, water outside the protoplast:

Figure 3 Key parameters of tissue water relations can be derived from pressure volume curves. By plotting the inverse of balancing pressure (as shown in (a)) the curve can be extrapolated to the x axis to obtain a value for water bound to cell walls (B) as well as a value for the inverse of osmotic pressure at saturation (P100), and at turgor loss point (P0) as well as RWC0 (identified where the curve st replica watches uk arts to become linear). In (b), the level of water stress imposed as water potential drops from saturation, 100, to turgor loss point, 0, creates a strain in the tissues which is registered as a reduction in cell volume from saturation (100) to RWC0. Lamont)

Preparation of pressure curves enables identication of a number of key water relations properties of plants. They show how different species and ecotypes respond to the same growing conditions, and how the same species changes its water relations properties as water availability changes (for example, see Table 1). These values are derived from pressure curves as shown in Figure 2. The osmotic potential of the vacuolar sap is more negative under the drier summer conditions than in winter. This means more solutes have been secreted into the vacuole, a response called osmotic adjust ment (P). In this case, P is ( = 0.82 MPa. The greater the plant ability to osmotically adjust, the greater its drought tolerance, for this increases its ability to maintain turgor and prevent desiccation. Drought tolerant plants usually have a lower P100, P0 and RWC0 than drought sensitive or drought avoiding plants. it drops below RWC0) it won necessarily die, for this may depend on the ability of the protoplast to withstand various levels of desiccation (see Feature essay 15.1). Against intuition, drought tolerant plants tend to have higher B and e. This is because their cells are smaller and have thicker, denser walls and smaller vacuoles, so that more water is apoplasmic and the cells are less elastic. (1992). An Instruction Manual for A Rapid, Accurate Program for Calculating and Plotting Water Relations Data Obtained from Pressure Studies, School of Environmental Biology, Curtin University: Perth.

Plants are active agents in new beauty products

Why people only ever hand over the flowers post row is a mystery for another columnist, because my puzzle this week is about skincare. In an increasingly tight market, beauty brands need to keep up to compete. That means being the first to discover the latest ingredients, and one of the biggest trends the industry has seen in recent years has been that of ethnobotany.

Skin scientists plunder far flung regions of the globe, suffering extremes of climate to bag ingredients, such as the Mediterranean pomegranate and the Siberian rhodiola herb.

Ethnobotany is big news and even bigger money and its latest harvest is that of flowers. At this point you’d be forgiven for sarcastically wondering “what next?” but according to Dr Lieve Declercq, the global spokesperson for plant physiology and molecular biology at Origins, a company with a mission to use naturally sourced ingredients, there’s a lot of history behind the rationale.

“Camomile flowers have been used as a remedy for a very long time,” she points out. As have the flowers of the echinacea plant. Origins is all about fin replica watches uk ding out what’s new and fab too, and a recent discovery the brand has made has been that of the power of the magnolia flower.

“Magnolia had been reported in scientific literature already,” Declercq adds, “so this triggered our attention and we thought it could work for us.”

Tests revealed that it is not just a pretty face. In fact, magnolia is a workhorse. “The major benefit is botanicals often perform multiple tasks as opposed to one single func replica watches uk tion, and this is the strongest we have ever used,” she says. Its abilities to control vascular permeability and the fact that it is a potent antioxidant have made it an ideal inclusion in Origins’ new GinZing Refreshing eye cream to brighten and depuff, 31 (see right).

I’m an eye cream sceptic, and if you read product claims closely, you’ll often come across the magical words “reduces the appearance of”. Now, that’s not the same as plain old fashioned reducing, and while the Origins product does contain some camouflaging and brightening ingredients in the form of silica and mica, it’s the magnolia that provides a point of difference.

Let me explain: those dark circles you see under your eyes are caused by blood pooling in the area and you tend to be able to see them so easily because the skin is very thin here.

“Dark circles are caused by blood vessels under the skin,” Declercq confirms. “When you are tired, they become leaky and because the tiny capillaries close to the surface in the eye area are very noticeable, you can really see them.”

This leaky thing is worrying: “The vessels let extra cellular fluid and blood out but we have found that magnolia makes the eye area less prone to this problem in the first place, and it controls that sensitivity and stabilises blood capillaries too,” Declercq explains.

Origins isn’t the only brand to sing the praises of magnolia. Guerlain, a company beloved of celebs such as Dita Von Teese and Elle Macpherson, has just launched Success Age Splendid, replica watches uk which uses magnolia extract as a key ingredient. Richard Hawkins, director of education and development at Guerlain, says that “the extract, derived from the magnolia flower, is able to restore the youthful functioning of mature skin allowing it to take on new life.”

Traditionally, the use of high end botanicals has been the preserve of small, luxury skincare lines: brands such as Darphin, Sisley, Chantecaille, Decleor and Guerlain lead the flower strewn charge. But difference is entering the industry, most noticeably from brands such as Liz Earle, Origins and even Garnier. That’s good news for consumers who don’t want to spend more than 100 on a pot of cream. But rest assured: if luxury lotions are your weakness, then you’ve plenty to choose from.

It’s not just facial skincare that contains the benefits of flowers. Botanical whizz Liz Earle uses piles of plants in her gorgeous, affordable products. Energising Hip and Thigh Gel, 24, uses geranium with toning and balancing properties, and is ideal for areas prone to cellulite. Earle has built a successful business on botanical extracts and says: “I am a big fan of their plumping, soothing and smoothing qualities.”

Garnier recently launched an orchid derived line, Vital Restore, aimed at women who are 50 plus and battling the effects of ageing and the menopause. I’ve got to ask, what’s so great about orchids, then?

“The orchid plant is endowed with a surprisingly long life span. Its secret lies in its capacity to pe replica watches uk rmanently renew its cells,” says the brand’s managing director of their international skincare labs, Anthony Potin.