Welcome to the Holbrook lab! We study the physics and physiology of vascular transport in plants with the goal of understanding how constraints on the movement of water and solutes between soil and leaves influences ecological and evolutionary processes. Currently, we are working on questions relating to cavitation, stomatal mechanics, leaf hydraulic design, and xylem evolution.

Holbrook Lab 2016
Lab photo 2016. Top row: Teressa Alexander, Cynthia Gerlein-Safdi, Greg Ceccantini, Jess Gersony, Alexandre "Pono" Ponomarenko, Walton "Tinker" Green. Bottom row: Nathan Mueller, Kadeem Gilbert, Fulton "Tony" Rockwell, Noel Michele "Missy" Holbrook, Uri Hochberg, Clement Quintard, Yongjiang "John" Zhang. Not pictured: Laura Clerx, Robinson "Wally" Fulweiler, Juan Losada, Bridget Power and Jessica Savage

Recent Publications

Knoblauch, Michael, Jan Knoblauch, Daniel L Mullendore, Jessica A Savage, Benjamin A Babst, Sierra D Beecher, Adam C Dodgen, Kaare H Jensen, and Noel Michele Holbrook. 2016. “Testing the Münch hypothesis of long distance phloem transport in plants.” eLife 5.Abstract

Long distance transport in plants occurs in sieve tubes of the phloem. The pressure flow hypothesis introduced by Ernst Münch in 1930 describes a mechanism of osmotically generated pressure differentials that are supposed to drive the movement of sugars and other solutes in the phloem, but this hypothesis has long faced major challenges. The key issue is whether the conductance of sieve tubes, including sieve plate pores, is sufficient to allow pressure flow. We show that with increasing distance between source and sink, sieve tube conductivity and turgor increases dramatically inIpomoea nil. Our results provide strong support for the Münch hypothesis, while providing new tools for the investigation of one of the least understood plant tissues.

Ronellenfitsch, H, J Liesche, KH Jensen, NM Holbrook, A Schulz, and E Katifori. 2015. “Scaling of phloem structure and optimality of photoassimilate transport in conifer needles.” Proc Biol Sci 282: 20141863.Abstract

The phloem vascular system facilitates transport of energy-rich sugar and signalling molecules in plants, thus permitting long-range communication within the organism and growth of non-photosynthesizing organs such as roots and fruits. The flow is driven by osmotic pressure, generated by differences in sugar concentration between distal parts of the plant. The phloem is an intricate distribution system, and many questions about its regulation and structural diversity remain unanswered. Here, we investigate the phloem structure in the simplest possible geometry: a linear leaf, found, for example, in the needles of conifer trees. We measure the phloem structure in four tree species representing a diverse set of habitats and needle sizes, from 1 (Picea omorika) to 35 cm (Pinus palustris). We show that the phloem shares common traits across these four species and find that the size of its conductive elements obeys a power law. We present a minimal model that accounts for these common traits and takes into account the transport strategy and natural constraints. This minimal model predicts a power law phloem distribution consistent with transport energy minimization, suggesting that energetics are more important than translocation speed at the leaf level.

Watkins, James E., Amber C. Churchill, and Noel Michele Holbrook. 2015. “A site for sori: Ecophysiology of fertile–sterile leaf dimorphy in ferns.” American journal of botany 103 (5): 845-855.Abstract

PREMISE OF THE STUDY: Reproduction often requires significant investment and can move resources away from growth and maintenance; maintaining a balance between reproduction and growth can involve trade-offs. Extreme functional specialization has separated reproduction and photosynthesis in most seed plants, yet ferns use the laminar surface of their fronds for both reproduction and photosynthesis. This dual function selects for a variety of frond morphologies that range from no specialization (monomorphy) to extreme dimorphy between fertile and sterile fronds (holodimorphy). Here we examined the ecological and physiological consequences of variation in frond dimorphy in ferns, evaluated reproductive trade-offs across a dimorphy gradient, and speculate on factors controlling the occurrence of holodimorphy.

METHODS: Ecophysiological measurements of photosynthetic rate, water potential, hydraulic conductivity, and gross morphological comparisons of frond area and angle were used to evaluate differences between fertile and sterile fronds. We examined three temperate and three tropical fern species that vary in degree of fertile–sterile dimorphy.

KEY RESULTS: Holodimorphic species produced fewer fertile fronds, which had significantly higher respiratory rates than in sterile fronds on the same plant or in any frond produced on monomorphic species; hemidimorphic species were frequently intermediate. We found no differences in vulnerability to cavitation between fertile and sterile fronds. In dimorphic species, fertile fronds had higher (less negative) water potential and lower stipe hydraulic conductivity relative than in sterile fronds.

CONCLUSIONS: Fertile–sterile dimorphy in ferns appears to come at considerable carbon cost in holodimorohic species. It is possible that the relative costs of this reproductive system are offset by increased spore dispersal, yet such trade-offs require further exploration.


Latest News

We will miss you, Teressa and Clem!!

We will miss you, Teressa and Clem!!

July 27, 2016

With a very heavy heart we sent off Teressa and Clement with a goodbye cake-and-wine party. After 2 years as an amazing research scholar in our lab (and an amazing friend!), Teressa is heading to Trinidad (University of the West Indies) to start a PhD program in plant physiology; and after a summer of terrific science and volleyball playing, "Clem" will be returning back to Europe to continue his Masters program. We wish them both the best and will miss them very, very much!!

Uri's paper in Tree Phys!

Uri's paper in Tree Phys!

July 15, 2016

Our post-doc and fearless volleyball coach, Uri Hochberg, published an awesome article in Tree Phys & got the cover! "Short-time xylem relaxation results in reliable quantification of embolism in grapevine petioles and sheds new light on their hydraulic strategy". Check it out! Link below.


Lab trip to Camp Xylem (and Phloem!) a.k.a. Gordon Research Conference

Lab trip to Camp Xylem (and Phloem!) a.k.a. Gordon Research Conference

July 1, 2016

What a great week!!! A majority of our lab (both current members and past members!) headed off to Newry, Maine for 5 days for a Gordon Research Conference about vascular plant biology. Not only did we engage in great conversations with people from all over the world who share our fascination (or dare I say, obsession) with the miracle that is plant vascular transport, we also got into nature quite a bit - we ate pie on top of a mountain, we swam in a waterfall, we paddle-boarded on a pond, we biked around rural Maine.... it was a dream of a trip! 


2016 Summer potluck picnic? Success!

June 14, 2016

On June 14th the lab got together on the Cambridge Public Library lawn for an awesome summer potluck picnic! Hopefully the first of many this summer! The (still undefeated!) Cavitators (volleyball team) also took this opportunity to further refine their legendary skills.